1.

If `cos^(2)theta-sin^(2)theta=(1)/(3)`, where, `theta(0 letheta le90^(@))`, the value of `co^(4)theta` is (यदि `cos^(2)theta-sin^(2)theta=(1)/(3)` और जहाँ `theta(0 letheta le90^(@))` का `co^(4)theta` मान ज्ञात करे)A. `(1)/(3)`B. `(2)/(3)`C. `(1)/(9)`D. `(2)/(9)`

Answer» Correct Answer - a
`3sin theta+5cos theta=5`
`5sin theta-3 cos theta=x`
now,
`a^(2)+ b^(2)=p^(2)+q^(2)`
`3^(2)+5 ^(2)=5^(2)+x^(2)`
`9+25=25+x^ (2)`
`9=x^(2)`
`x=+-3`


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