RRB JE Stage I 23 May 2019 Shift 1 (HM)

Question : 5 of 100

Marks: +1, -0

\cos ^{4} {A}-\sin ^{4} {A}

का मान ज्ञात कीजिए।

Solution:

\cos ^{4} {A}-\sin ^{4} {A}

=(\cos ^{2} {A})^{2}-(\sin ^{2} {A})^{2}

=(\cos ^{2} {A}+\sin ^{2} {A})(\cos ^{2} {A}-\sin ^{2} {A})

=\cos 2 {A}

[\∵ \cos ^{2} {A}+\sin ^{2} {A}=1]

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