Question

a) x² -900

b)16x²-y²

c)64-25a²

Answer 1

a) 

x² - 900 = 0
x² = 900
x = √900
x' = 30
x'' = -30

b)
16x² - y² = 0
16x² = y²
x² = y²/16
x = √y²/16
x = y/4

c)
64 - 25a² = 0
64 = 25a²
a² = 64/25
a = √64/25
a = 8/5                                       ok