Answer:
Step-by-step explanation:
10) Cos (x-y) = cos x cos y + sin x sin y
cos 4x cox 3x + sin 4x sin 3x = Cos (4x - 3x)
= cos x
11) = 2*(1² + 2) + 2*(2² + 2²)
= 2*3 + 2*(4+4)
= 6 + 2*8
= 6 + 16
= 22
12) (3) 4x² - 3x - 8 = 0
Reason:
Sum of roots = - Coefficient of x/coefficient of x² = -(-3)/4 = 3/4
Product of roots = constant / coefficient of x² = -8/4 = -2
