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

question 39

Essay

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

---

Definitions:

Applied Research

It is a form of systematic inquiry involving the practical application of science. It is used for solving problems and inventing new processes and products.

Resource Productivity

The measure of how effectively economic resources are used to produce goods and services.

Immediate Payoff

The immediate benefits or rewards derived from a particular action or decision.

Basic Research

Research conducted to increase fundamental knowledge and understanding, without a specific practical aim or application.