ACOS in SoftMaker PlanMaker 2026: examples and troubleshooting

Arccosine answers: “Which principal angle has this cosine?” The mathematical principal output is between 0 and π radians (0° to 180°). A cosine does not uniquely identify an arbitrary oriented angle, because cosine is even and periodic. SoftMaker documents ACOS(1)=0 and ACOS(COS(0.1234))=0.1234 as examples; those do not establish universal recovery of all original angles.

Use this function when the quantity being calculated and its units match the mathematical role described. The PlanMaker 2026 function reference is the evidence for the function’s actual PlanMaker name, parameter meaning, and unit conventions. Worked applications are explicitly derived from mathematics; their numeric outputs have not been confirmed by launching PlanMaker.

=ACOS(Number)

No optional parameters and no defaults are documented. The capitalization of the displayed parameter name is not a second function or alias. The English manual lists the function as ACOS; there is no documented alternate English function name on the referenced 2026 or 2024 entry. Start spreadsheet formulas with =. English-language examples use decimal points; decimal separators and function-name translations should be checked in the target installation rather than assumed. As this function takes a single argument, the primary syntax uses no list-separator comma or semicolon. The formula-entry instructions explain using the function dialog to check a local installation. PlanMaker 2026; PlanMaker 2024 (checked 2026-10-13).

Start a blank worksheet. Put each number in column A of the matching row, then enter the B and C formulas as shown. The final column below is an independently computed comparison, not a value read from PlanMaker.

Enter the numeric cosine ratios in A2:A7. Put the formulas in B2:B7 and C2:C7, then format C with your desired decimal places. Comparing a computed value to an integer degree should allow normal floating-point tolerance. Column B contains radians even when column C displays degrees; format changes do not convert units.

How to verify: type the inputs as numbers, enter formulas with =, and compare the displayed values with the expectations at sensible precision. Different display formats and finite-precision arithmetic can change the final decimal places. Numeric display formatting does not change whether an angle is radians or degrees. The source formulas and output-unit requirement are documented by SoftMaker ACOS; output values other than the vendor’s explicit example were mathematically calculated independently.

• =ACOS(1) → independently expected 0 (independently computed mathematical expectation, not a PlanMaker runtime test).
• =ACOS(-0.5) → independently expected 2.09439510239 (independently computed mathematical expectation, not a PlanMaker runtime test).
• =DEGREES(ACOS(0.28)) → independently expected 73.7397952917 (independently computed mathematical expectation, not a PlanMaker runtime test).

Angle opposite a side via the law of cosines

A triangle has sides a = 5, b = 5 and an opposite side c = 6. Put 5, 5, 6 into E2, F2, G2 respectively. To compute the included angle between sides a and b:

=DEGREES(ACOS((E2^2+F2^2-G2^2)/(2*E2*F2)))

The cosine argument independently becomes (25 + 25 − 36)/50 = 0.28. The expected angle is approximately 73.7397952917°. First verify that triangle side lengths are positive and meet the triangle inequality; invalid side combinations can make the computed ratio outside −1 to 1.

Right triangle validation

For 3–4–5 sides, the angle opposite the length-5 side satisfies cos(C)=(3^2+4^2−5^2)/(2·3·4)=0. Therefore =DEGREES(ACOS(0)) independently equals 90°. This gives a useful diagnostic for a right-angle geometry formula.

Cosine cannot determine orientation by itself

Both +60° and −60° have cosine 0.5. =DEGREES(ACOS(COS(RADIANS(-60)))) independently yields 60°, not −60°. If direction or quadrant matters, use additional sign information or inspect ATAN2 rather than treating ACOS as a full signed-bearing calculation.

Handle data near the domain boundary

A ratio slightly greater than 1 or less than −1 may come from a measurement issue or an unstable formula. Because ACOS’s documented input is strictly constrained to [−1, 1], first inspect the upstream values. Do not hide genuine geometry problems by applying an unexamined clamp.

ACOS requires one numeric argument; there are no optional arguments or defaults. Its documented input domain includes both −1 and 1. Inverse cosine on a real number gives the principal angle, not a globally unique directional angle. The specific error display for each bad input was not natively tested in PlanMaker.

PlanMaker’s official 2026 error-values guide identifies #NUM! as an invalid numerical input, #VALUE! as an inappropriate argument type, #NULL! as an invalid formula or function signature, and #DIV/0! as division by zero. These are general documented categories, not claims that each particular formula in this review was executed to observe a particular error display. Never copy an Excel-specific error code into a PlanMaker guide without checking the vendor documentation first. (PlanMaker error values, checked 2026-10-13).

For .xlsx interchange, compare results on representative numeric inputs in both applications before treating a production workbook as validated. No workbook was opened, converted, saved, or executed in either PlanMaker or Excel during this research run.

• Official SoftMaker PlanMaker 2026 ACOS reference — syntax, purpose, and the vendor’s worked example.
• Official SoftMaker PlanMaker 2024 ACOS reference — separate version cross-check.
• Official PlanMaker 2026 COS — cosine — vendor documentation.
• Official PlanMaker 2026 DEGREES — convert radians to degrees — vendor documentation.
• Official PlanMaker 2026 SIN — sine — vendor documentation.
• Official PlanMaker 2026 ATAN2 — two-coordinate arctangent — vendor documentation.
• Official PlanMaker 2026 PI — π constant — vendor documentation.
• PlanMaker 2026 formula-entry help — entering and editing a formula.
• PlanMaker 2026 error-values help — PlanMaker-specific error categories.
• Microsoft Excel ACOS reference — separate vendor’s function documentation.

Reference-check date: 2026-10-13. PlanMaker 2026 and PlanMaker 2024 function pages were reviewed separately, as were the current SoftMaker general help pages and the Microsoft Excel reference. All example values are independently calculated, using elementary mathematical identities and Python’s math routines as appropriate. This is not a native SoftMaker result.

Validation matrix: PlanMaker 2026: 0 native formula executions; PlanMaker 2024: 0; PlanMaker NX: 0; Excel: 0; other editions/platforms: 0; screenshots: 0; Excel import/export checks: 0.