Question

(4x+5)(4x-1) with appropriate identity find it?

Answer 1

The right answer.
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Answer 2

We know that,
$(x + a)(x + b) = x {}^{2} + (a + b)x + ab$
By using this formula,we get

$(4x + 5)(4x - 1) =(4x {})^{2} + (5 - 1)4x + 5 \times ( - 1) \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 16x {}^{2} + 4 \times 4x - 5 \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 16 {}^{2} + 16x - 5$