Question

Giúp mik giải cho cos x=1/2.Tìm biểu thức P=3sin^2x+1 A 13/4 B 7/4 C 11/4 D 15/4

Answer 1

`sin^2x+cos^2x=1`

`<=>sin^2x+(1/2)^2=1`

`<=> sinx=\pm \sqrt3/2`

• `sinx=\sqrt3/2 => P=3. (\sqrt3/2)^2 +1=13/4`

• `sinx=-\sqrt3/2 => P = 3.(-\sqrt3/2) +1=13/4`

`=>` A.

Answer 2

\(P=3sin^2x+1=3\left(1-cos^2x\right)+1=3\left(1-\dfrac{1}{4}\right)+1=\dfrac{13}{4}\)