d) 5^(x-2).(x+3)=1
<=>5^(x-2).(x+3)=5^0
<=>(x-2).(x+3)=0
<=>
x-2=0=>x=2
x+3=0=>x=-3
Vậu x thuộc {2;-3}
Bài 5.
A=1.2+2.3+3.4+...+99.100
3A= 1.2.3+2.3.3+3.4.3+...+99.100.3
3A=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+...+99.100.(101-98)
3A=(1.2.3+2.3.4+3.4.5+...+99.100.101)-(0.1.2+1.2.3+2.3.4+...+98.99.100)
3A=99.100.101-0.1.2
3A=99.100.101-0
3A=999900
A=999900:3
A=333300
Vậy A=333300
Cho ctlhn và 5 sao nha
