Question

suitable identities:(x+1)(x+3)​

Answer 1

Answer:

$(x + a) (x + b) = {x }^{2} + (a + b)x + ab \\ here \: x = x \: and \: a = 1 \: and \: b = 3 \\ (x + 1)(x + 3) = x {}^{2} + (1 + 3)x + (1)(3) \\ (x + 1)(x + 3) = x {}^{2} + 4x + 3 \\( x + 1)(x + 3) = {x}^{2} + x + 3x + 3 \\( x + 1)(x + 3) =x(x + 1) + 3(x + 1) \\ ( x + 1)(x + 3) =(x + 1)(x + 3)$

Therefore, LHS = RHS

So here, the identity used is

x + a) (x + b) = {x }^{2} + (a + b)x + ab