1. Tìm x:
a) 2^x-7 – 3 = 29
b) 2^3 . 3 + 286 : (x-3) = 50
c) 9^x + 19 = 4.5^2
2. Tính hợp lí:
a) 60 . 7 + 70 . 94 – 35 . 94
b) 4.35.25 + 2.17.50 – 460.5
c) 18.54 + 49.18 – 103.8
1. Tìm x:
a) 2^x-7 – 3 = 29
b) 2^3 . 3 + 286 : (x-3) = 50
c) 9^x + 19 = 4.5^2
2. Tính hợp lí:
a) 60 . 7 + 70 . 94 – 35 . 94
b) 4.35.25 + 2.17.50 – 460.5
c) 18.54 + 49.18 – 103.8
Bài 1:
` a) ` ` 2^{x – 7} – 3 = 29 `
` => 2^{x – 7} = 29 + 3 `
` => 2^{x – 7} = 32 `
` => 2^{x – 7} = 2^5 `
` => x – 7 = 5 `
` => x = 12 `
` b) ` ` 2^3. 3 + 286 : (x – 3) = 50 `
` => 8.3 + 286 : (x – 3) = 50 `
` => 286 : (x – 3) = 50 – 8.3 `
` => 286 : (x – 3) = 50 – 24 `
` => 286 : (x – 3) = 26 `
` => x – 3 = 286 : 26 `
` => x – 3 = 11 `
` => x = 11 + 3 `
` => x = 14 `
` c) ` ` 9^x + 19 = 4.5^2 `
` => 9^x + 19 = 100 `
` => 9^x = 100 – 19 `
` => 9^x = 81 `
` => 9^x = 9^2 `
` => x = 2 `
Đáp án:
Giải thích các bước giải:
1.
a) 2^(x – 7) – 3 = 29
2^(x – 7) = 29 + 3
2^(x – 7) = 32
2^(x – 7) = 2^5
x – 7 = 5
x = 12
b) 2^3. 3 + 286 ÷ (x – 3) = 50
8.3 + 286 ÷ (x – 3) = 50
286 ÷ (x – 3) = 50 – 8.3
286 ÷ (x – 3) = 50 – 24
286 ÷ (x – 3) = 26
x – 3 = 286 ÷ 26
x – 3 = 11
x = 11 + 3 = 14
9^x + 19 = 4.5^2
9^x + 19 = 100
9^x = 100 – 19
9^x = 81
9^x = 9^2
x = 2
2.
a) 60.7 + 70.94 – 35.94
= 12.5.7 + 94.(70 – 35)
= 12.35 + 94.35
= (12 + 94).35 = 106.35 = 3710
b) 4.35.25 + 2.17.50 – 460.5
= 2.2.35.25 + 34.50 – 46.10.5
= 70.50 + 34.50 – 46.50
= (70 + 34 – 46). 50 = 58.50 = 2900
c) 18.54 + 49.18 – 103.8
= 18.(54 + 49) – 103.8
= 18.103 – 103.8
= (18 – 8).103 = 10.103 = 1030