Prove (2cosa+1)(2cosa-1)=2cos4a+1

Can (2,3 and square root 10) be sides ona right triangle?

Find the gradient of f(x,y,z)equals=left parenthesis x squared plus y squared plus z squared right parenthesis superscript negative 1 divided by 2 baseline plus ln left parenthesis x right parenthesis x2+y2+z2−1/2+ln(xyz) at the point left parenthesis negative 2 comma 1 comma negative 2 right parenthesis(−2,1,−2).

The two square pyramids are similar. find the total volume of both pyramids if the ratio of their surface areas is 9/16