Evaluate the sum of two angles with cosine

👉 Learn how to evaluate the cosine of an angle in radians using the sum/difference formulas. To do this, we first express the given angle as a sum or a difference of two (easy to evaluate) angles, then we use the unit circle and the Pythagoras theorem to identify the angles and obtain all the needed trigonometric function values of the angles. When we know the trigonometric function values of the two angles to be added or subtracted, we can apply the sum and difference formulas to evaluate the cosine of the given angle.

Organized Videos:
✅ Sum and Difference Formulas
✅ Evaluate Sum and Difference Formulas from a Triangle
✅ Simplify an Expression using Sum and Difference Formulas
✅ Write the Expression as a single function | Sum and Difference Formulas
✅ Verify Identities using Sum and Difference Identities
✅ Evaluate Tangent using Sum and Difference Formulas
✅ Evaluate Cosine using Sum and Difference Formulas
✅ Evaluate Sine using Sum and Difference of Two Angles
✅ Solve Equations using Sum and Difference Formulas

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[maahir.sharma]

Also back here in India we studied this grade 10th.Was kinda surprising for me to find this being taught in highschool but props to you for teaching so patiently.

[maahir.sharma]

What I did here is was that I converted the radian into degrees and got it as 285°.
Now I used cos(90+theta) and got the answer as 0.255 which is equivalent to your answer is this approach correct.
Because cos(a+b) would take a lotta time.

[maahir.sharma]

Also if we had to find cos(285°) why dont dont you apply the formula cos(theta)= ??