The value of cos( tan^ -1 (tan (15π/4))) is (a) -1/√2 (b) 0 (c)1/√2 (d)1/2√2
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so the tan^-1 will cancel tan
then the question is cos(15π/4)
now it can be written as cos(3π+3π/4)
and it is equal to cos3π/4
it can also be written as cos(π-π/4)
and we know cos(π-π/4)=-cosπ/4
so answer is -1/√2
then the question is cos(15π/4)
now it can be written as cos(3π+3π/4)
and it is equal to cos3π/4
it can also be written as cos(π-π/4)
and we know cos(π-π/4)=-cosπ/4
so answer is -1/√2
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