Question

(sin72+cos18)(sin72-cos18)

Answer 1

=sin2 72-cos2 18
=(cos 90-18)2 -cos2 18
=cos2 18-cos2 18
=0

Answer 2

Answer:

$value \: of \:,\\(sin72+cos18)(sin72-cos18)\\=0$

Step-by-step explanation:

$Given ,\\(sin72+cos18)(sin72-cos18)\\=sin^{2}72-cos^{2}18$

/* By algebraic identity:

(a+b)(a-b)=a²-b²/ */

$=[sin(90-18)]^{2}-cos^{2}18\\=(cos18)^{2}-cos^{2}18\\=cos^{2}18-cos^{2}18\\=0$

Therefore,

$value \: of \:,\\(sin72+cos18)(sin72-cos18)\\=0$

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