Buku Matematika Peminatan Sukino Kelas X
Bab 1 Fungsi, Persamaan, dan Pertidaksamaan Eksponensial
LKS 5
Soal dan Jawaban Matematika Kelas X Sukino
Kunci Jawaban Matematika Sukino
3. Selesaikan setiap sistem persamaan eksponensial berikut.
a. 3x - 4y = 5
3x + 1+ 4y = 23
b. 2x - 5y = 3
2x - 3= 21 - 5y - 2
c. 2 . 5x + 1 = 4 . 2-y
5x = 2 . 2y
d. 53x / 25y = 3125
2x . 4y - 1 = 32
Jawaban :
a. 3x - 4y = 5
3x + 1+ 4y = 23
misalkan :
3
x = a
4
y = b
3
x - 4
y = 5
a - b = 5 ... (i)
3
x + 1+ 4
y = 23
3a + b = 23 ... (ii)
menggunakan eliminasi
a - b = 5
3a + b = 23
--------------- +
4a = 28
a = 7
a - b = 5
7 - b = 5
b = 2
a = 7
3
x = 7
x = 3log 7
b = 2
4
y = 2
2
2y = 2
0
2y = 0
y = 0
-------------------------------------------------------
b. 2x - 5y = 3
2x - 3= 21 - 5y - 2
misalkan :
a = 2
x
b = 5
y
2
x - 5
y = 3
a - b = 3 ... (i)
2
x - 3= 21 - 5
y - 2
1/3 a = 21 - 1/25 b ... (ii)
menggunakan eliminasi (i) x 125 dan (ii) x 1000
125a - 125b = 375
125a + 40b = 21000
------------------------- -
- 165b = - 20625
b = 125
5
y = 125
5
y = 5
3
y = 3
masukan ke dalam salah satu persamaan :
a - b = 3
a = 3 + 125
a = 128
2
x = 2
7
x = 7
------------------------------------------
c. 2 . 5x + 1 = 4 . 2-y
5x = 2 . 2y
misalkan :
a = 5
x
b = 2
y
2 . 5
x + 1 = 4 . 2
-y
2 . 5 a = 4 . 1/b
10 a = 4/b
a = 4/10b
a = 2/5b
5
x = 2 . 2
y
a = 2 . b
2/5b = 2b
2 = 10 b
2
1/5 = b
2
b = 5
-1/2
2
y = 5
-1/2
y =
2log 5
-1/2
y = -1/2
2log 5
masukan ke dalam persamaan :
a = 2/5b
a = 2/(5. 5
-1/2)
5
x= 2/5
1/2
x =
5log 2 . 5
-1/2
x =
5log 2. 5
-1/2
x =
5log 2 +
5log 5
-1/2
x =
5log 2 - 1/2
-----------------------------------------------------------------
d. 53x / 25y = 3125
2x . 4y - 1 = 32
5
3x / 25
y = 3125
5
3x / 5
2y = 5
5
5
3x 5
-2y = 5
5
3x - 2y = 5 ... (i)
2
x . 4
y - 1 = 32
2
x . 2
2(y - 1) = 2
5
x + 2y - 2 = 5
x + 2y = 7 ... (ii)
menggunakan eliminasi
3x - 2y = 5
x + 2y = 7
--------------- +
4x = 12
x = 3
masukan ke dalam persamaan (ii)
x + 2y = 7
3 + 2y = 7
2y = 4
y = 2
>>Soal B no 4