Prove $\cos \left( x + \frac { \pi } { 4 } \right) + \cos \left( x - \frac { \pi } { 4 } \right) = \sqrt { 2 } \cos x$

Q34: Solve the given equation. <span

Q35: Verify the identity. <span class="ql-formula"

Q36: Make the indicated trigonometric substitution in

Q37: Prove <span class="ql-formula" data-value="\sin (

Q38: Find all solutions of <span

Q40: Write the product as a sum.

Q41: Use a half-angle formula to find

Q42: Use addition or subtraction formulas to

Q43: Use an addition or subtraction formula

Q44: Find all solutions of <span