Answer :
10a^2-10 = 630
10(a^2 - 1) = 630
(a^2 - 1) = 630/10
a^2 - 1 = 63
a^2 = 63 + 1
a^2 = 64
a = +- 8
10(a^2 - 1) = 630
(a^2 - 1) = 630/10
a^2 - 1 = 63
a^2 = 63 + 1
a^2 = 64
a = +- 8