f(x) = 6x3 - 8x2 + 21
f'(x) = (6x3 - 8x2 + 21)' = 18x2 - 16x
f'(-2) = 18(-2)2 - 16(-2) = 18(4) + 32 = 72 + 32 = 104
f(-2) = 6(-2)3 - 8(-2)2 + 21 = 6(-8) - 8(4) + 21 = -48 - 32 + 21 = -80 + 21 = -59
y - f(x0) = f'(x0)(x - x0)
y - (-59) = 104(x - (-2))
y + 59 = 104(x + 2)
y + 59 = 104x + 208
y = 104x + 208 - 59
y = 104x + 149
Ответ: y = 104x + 149