Найти sin в если cos в = - 7/15

По основному тригонометрическому тождеству sin^2b + cos^2b = 1.

cosb = - 7/15;

cos^2b = (-7/15) ^2 = 49/225;

sin^2b = 1 - cos^2b;

sin^2b = 1 - 49/225;

sin^2b = 225/225 - 49/225;

sin^2b = (225 - 49) / 225;

sin^2b = 176/225;

sinb = + -sqrt (176/225);

sinb = + -sqrt (16 * 11) / 15;

sinb = + -4sqrt11/15.