Question

Tìm x biết:

\(a,18:(x-3)=6\)

\(b,\)\(3^{x-1}+4=85\)

\(c,2x+3x=55\)

\(\left(x-3\right)^3+11=53\)

Answer 1

a: 18:(x-3)=6

=>x-3=18:6=3

=>x=3+3=6

b: \(3^{x-1}+4=85\)

=>\(3^{x-1}=81\)

=>\(3^{x-1}=3^4\)

=>x-1=4

=>x=5

c: 2x+3x=55

=>5x=55

=>x=55/5=11

d: \(\left(x-3\right)^3+11=53\)

=>\(\left(x-3\right)^3=53-11=42\)

=>\(x-3=\sqrt[3]{42}\)

=>\(x=\sqrt[3]{42}+3\)

Answer 2

a) 18 : (x - 3) = 6

x - 3 = 18 : 6

x - 3 = 3

x = 3 + 3

x = 6

b) 3ˣ⁻¹ + 4 = 85

3ˣ⁻¹ = 85 - 4

3ˣ⁻¹ = 81

3ˣ⁻¹ = 3⁴

x - 1 = 4

x = 4 + 1

x = 5

c) 2x + 3x = 55

5x = 55

x = 55 : 5

x = 11

d) Sửa đề:

(x - 3)³ - 11 = 53

(x - 3)³ = 53 + 11

(x - 3)³ = 64

(x - 3)³ = 4³

x - 3 = 4

x = 4 + 3

x = 7