1.

निम्नलिखित के मुख्य मानों को ज्ञात कीजिए - `cos^(-1)(-(1)/(sqrt2))`

Answer» माना `cos^(-1)(-(1)/(sqrt2))=theta`
`rArr" "cos theta=-(1)/(sqrt2)," "theta in [0,pi]`
`rArr" "cos theta=-cos.(pi)/(4)`
`rArr" "cos theta=cos(pi-(pi)/(4))`
`" "[because cos (pi-theta)=-cos theta]`
`rArr" "cos theta = cos.(3pi)/(4)`
`rArr" "theta=(3pi)/(4)`
अतः `cos^(-1)(-(1)/(sqrt2))` का मुख्य मान `(3pi)/(4)` है।


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