If x is an acute angle, which expressions is not equivalent to cosx?

Which expression is equivalent to (9x^(2)y^(6))^(-(1)/(2)) ?

The expression x^(2)-7x+12 is equivalent to :

Which of the following expressions is equivalent to -x^(1/4) ?

Which of the following expressions is equivalent to (9x+45)/9 ?

Which of the following expressions is equivalent to 49x^(2) + 81 ?

Which of the following expression is equivalent to (sin^(2)x)/(1+cosx) ?

Prove the following identity, where the angles involved are acute angles for which the expressions are defined. (i) (cosectheta-cottheta)^2=(1-costheta)/(1+costheta)

Prove the following identity, where the angles involved are acute angles for which the expressions are defined. (v) (cosA-sinA+1)/(cosA+sinA-1)=cosec A+cotA

Prove the following identities, where the angles involved are acute angles for which the expressions are defined. : (cosec A -sin A) (sec A - cos A) = sin A.cos A

Prove the following identities, where the angles involved are acute angles for which the expressions are defined. : (cosectheta-cottheta)^2=(1-costheta)/(1+costheta) .