Matematika

Pertanyaan

1. Misalkan f(x)= sin(sinx.cosx), maka f'(x)= . . .
a. cos(sinx.cosx)
b. sin (cos^2 x -sin^2 x)
c. cos (sin x). cos x(cos x)
d. cos 2x. cos (sinx.cosx)

2. jika garis singgung dari kurva y= px^3 - qx^2 + 1 di x=2 adalah y-2x+5=0, maka 2pq = . . .
a. 5
b. 4
c. 3
d. 2
e. 1

2 Jawaban

  • 2 sin x cos x = sin 2x => sin x cos x = 1/2 sin 2x

    1) f(x) = sin (sin x cos x) = sin (1/2 sin 2x)
    f'(x) = cos (1/2 sin 2x) . 1/2 cos 2x . 2
    = cos 2x . cos (1/2 sin 2x)
    = cos 2x . cos (sin x cos x)

    2) y - 2x + 5 = 0
    => y = 2x - 5 => m = 2
    x = 2 => y = 2(2) - 5 => y = -1

    (2, -1)
    y = px^3 - qx^2 + 1
    -1 = p(2)^3 - q(2)^2 + 1
    -1 = 8p - 4q + 1
    -8p + 4q = 2
    -4p + 2q = 1

    y = px^3 - qx^2 + 1
    y' = 3px^2 - 2qx
    m = y'
    2 = 3p(2)^2 - 2q(2)
    2 = 12p - 4q
    1 = 6p - 2q

    Eliminasi
    -4p + 2q = 1
    6p - 2q = 1
    ----------------- +
    2p = 2 => p = 1

    -4p + 2q = 1
    -4(1) + 2q = 1
    2q = 5
    q = 5/2

    2pq = 2(1)(5/2) = 5
  • 1) misalkan U=sin x. cos x
    Mk U' = cos²x - sin²x
    f(x) = sin U
    f'(x) = U' cos U = (cos²x-sin²x) cos(sin x. cos x) = cos 2x cos (sin x.cos x) (D)

    2) y-2x+5 = 0 masukkan x=2 mk di dpt y = - 1
    Masukkan (2,-1) ke y=px³-qx²+1 mk di dpt 8p-4q+1 = - 1 atau 8p-4q = - 2
    y' = 3px²-2qx masukkan x=2 shg y'=12p-4q
    y-2x+5=0 memiliki gradien = 2
    Mk 12p-4q = 2
    Eleminasi 8p-4q = - 2 dengan 12p-4q = 2 akan di dapat 4p = 4 atau p=1
    p=1 —> 8-4q = - 2 —> q = 2½
    2pq = 2.1.2½ = 5 (A)

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