tolong berikan pejelasan dan penjabaran , terimakasih

7-10 sudah terjawab ya di pos soal lain

12) m = (y2 - y1)/(x2 - x1)
mPQ . mQR = -1
(2 - a)/(9 - 3) . (11 - 2)/(3a - 9) = -1
(2 - a)/6 . 9/(3a - 9) = -1
(18 - 9a)/(18a - 54) = -1
18 - 9a = -18a + 54
9a = 36
a = 4
P(3,4), Q(9,2), R(12,11)
PQ = √((3 - 9)^2 + (4 - 2)^2) = √(36 + 4) = √40 = 2√10
QR = √((9 - 12)^2 + (2 - 11)^2) = √(9 + 81) = √90 = 3√10
Luas segitiga = 1/2 . PQ . QR = 1/2 . 2√10 . 3√10 = 30

13) f(x) = 1/8 x - 3, g(x) = x^3
1) (f o g)(x) = f(g(x)) = f(x^3) = 1/8 x^3 - 3 ==> BENAR
2) (f o g)(2) = 1/8 . 2^3 - 3 = 1 - 3 = -2 ==> BENAR
3) misal 1/8 x^3 - 3 = y
=> 1/8 x^3 = y + 3
=> x^3 = 8y + 24
=> x = ^3√(8y + 24)
=> (f o g)^-1(x) = ^3√(8x + 24) ===> BENAR
4) (f o g)^-1(-2) = ^3√(8(-2) + 24) = ^3√(8) = 2 ==> BENAR

14) y = x^3 - 4x^2 + 3x
m = 6 => y' = m
=> 3x^2 - 8x + 3 = 6
=> 3x^2 - 8x - 3 = 0
=> (3x + 1)(x - 3) = 0
=> x = -1/3 atau x = 3
(2) dan (4)