Given:

f(x) is continuous at x = & f() = a,

If f(x) to be continuous at x = ,we have to show, f()^– ₌ f() ⁺ ₌ f()

LHL = f()^– =

sin(–x) = cosx

cos(–x) = sinx

(a³–b³) = (a–b)(a² + ab + b²)

∴ cos(0) = 1

...(1)

LHL = f() ⁺ =

1

...(2)

f(x) is continuous at x = & f() = a ,and from (1) & (2),we get

f()^– ₌ f() ⁺ ₌ f()

= a

a =

⇒ b = 4

Hence ,a = & b = 4