a) 3/4-3/4:x=1/2
=>3/4:x=3/4-1/2
=>3/4:x=3/4-2/4
=>3/4:x=1/4
=>x=3/4:1/4
=>x=3/4.4/1
=>x=4
b)-12.(x-5)+7.(3-x)=5
=>-12x+60+21-7x=5
=>81-19x=5
=>19x=81-5
=>19x=76
=>x=76:19
=>x=4
c) |7x+3|=66
=>7x+3=-66 hoặc 7x+3=66
+)Nếu 7x+3=-66
=>7x=-66-3=-66+(-3)=-69
=>x=(-69):7=\(\frac{-69}{7}\)
+)Nếu 7x+3=66
=>7x=66-3=63
=>x=x=63:7=9
d)(x-7)(x+3)<0
=>x-7<0 hoặc x+3<0
+)/nếu x-7<0
=>x<7
+)nếu x+3<0
=>x<-3