Question

[minh van angela]

ai dc ng do la ng thong minh vi day la bai toan cho hoc sinh gioi toan [chu y:day chi la dang toan loai kha thui nha]

tim x

3^x =81

2^x+3 +2^x=144

x^2 - 4x=0

thc hien phep tinh

(5^4 + 4^7)  (8^9-2^7) (2^4 - 4^2)

4^3.51+4^3.49+2.(3^2 +4^2 )

tim n,biet

3^n+3  + 3^n =252

z thui   phai giai het moi chon nha                                   chi dc sai 2 cau la toi da

Answer 1

[Võ Nguyễn Thùy Huyên]

a) vì 81=3⁴=(-3)⁴

=> x=3

hoặc x=-3

b) 2^x+3 +2^x=144

=> 2^x.2³+2^x=144

=>2^x.(2³+1)=144

=>2^x.9=144

=>2^x=144:9=16

mà 16=2⁴

=> x=4

c)x²-4x=0

=>x.(x-4)=0

=> x=0

hoặc x-4=0 => x=4

=> x=0

hoặc x=4

d)(5^4 + 4^7)  (8^9-2^7) (2^4 - 4^2)

=(5^4 + 4^7)  (8^9-2^7) .(16-16)

=(5^4 + 4^7)  (8^9-2^7) .0

=0

e)4^3.51+4^3.49+2.(3^2 +4^2 )

=4³.(51+49)+2.(9+16)

=64.100+2.25

=6400+50

=6450

f)3ⁿ⁺³+3ⁿ=252

3ⁿ.3³+3ⁿ=252

3ⁿ.(3³+1)=252

3ⁿ.28=252

=>3ⁿ=252:28=9

mà 9=3²

=>x=2