If an equation is an identity, then how many solutions does it have?

In the figure shown below, m < 40 and ab =8. which equation could be used to find x?

Find the magnitude, correct to two decimal places, made by each of the following with positive direction of the x axis a) y= x the answer is 45° but i don’t know how

Suppose a gym membership has an initial enrollment fee of $75 and then a fee of $29 a month. which equation models the cost, c, of the gym membership for m months?