Answer:
see explanation
Explanation:
using the identity
sin²x + cos²x = 1
consider left side
(cosA - sinA)²
= (cosA - sinA)(cosA - sinA) ← expand using FOIL
= cos²A - sinAcosA - sinAcosA + sin²A
= cos²A + sin²A - 2sinAcosA
= 1 - 2sinAcosA
= right side