Step-by-step explanation:
We will use the LHS to find the RHS.
Step 1: Expand the LHS by multiplying through the brackets and simplify
(sinx + cosx)(1 − sinx cosx) ≡ sinx + cosx - (sinx + cosx (sinx cosx))
≡ sinx + cosx - sin²x cosx - sinx cos²x
Step 2: Use the identity sin²x + cos²x = 1, to rewrite the equation
≡ sinx + cosx - cosx (1 - cos²x) - sinx (1 - sin²x)
Step 3: Simplify the equation by adding like terms
≡ sinx + cosx - cosx + cos³x - sinx + sin³x
≡ sin³x + cos³x [QED]
Reminder:
