2st squared -s squared.

S=4 t=8

just plug in the values:

2(4)(8^2) - 4^2
8*64 - 16
496

To evaluate the expression 2st^2 - s^2 when s = 4 and t = 8, you would need to substitute the given values of s and t into the expression and then simplify.

Start by substituting s = 4 and t = 8 into the expression:
2(4)(8^2) - 4^2

Now simplify the expression:
2(4)(64) - 16
8(64) - 16
512 - 16 = 496

Therefore, when s = 4 and t = 8, 2st^2 - s^2 equals 496.