`1.`
`a,20: 2^2+5^19 :5^17`
`=20:4+5^19 -17`
`=5+5^2`
`=5+25`
`=30`
`b,|-2017|+[3^2 .15-(9-5)^2]`
`=2017+[9.15-16]`
`=2017+[135-16]`
`=2017+119`
`=2136`
`c,(-3).{150-[2^3 . 3^2 -(7-15)^2]}=-426`
`=(-3).{150-[8.9-(-64)]}`
`=(-3).{150-[72+64]}`
`=(-3).{150-136}`
`=(-3).14`
`=-42`
`2.`
`a,28+2(x-3)=50`
`2(x-3)=22`
`x-3=11`
` x =14`
`b,6+3^{x+2}=87`
`3^{x+2}=81`
`3^{x+2}=3^4`
`x+2=4`
`x =2`
`3.`
a,Số học sinh lớp `6A` là:
`20+14-7+5=32(HS)`
b,Ta có:`ƯCLN_((130,132))`
`130=2.5.13`
`132=2^2 .5.13`
`=>ƯCLN_((130,132))=2.5.13=130`
Vây `x=130`