to find LCM of exg 6 and 21, find factors and group 6=2 and 3 (one 2 and one 3) 21=3 and 7 (one 3 and one 7) lcm=2 and 3 and 7 (include 6 and 21 in the number) (one 2 and one 3 and one 7)
LCM≈LCD so 17. denomenators are 2 and x^2 2=2 x^2=x times x lcm=2 times x times x=2x^2
18. denomenators are 6 and 9 6=2 and 3 9=3 and 3 LCM=2 times 3 times 3=18
19. denomenators are z and 7z z=z 7z=7 and z lcm=7 times z=7z
20. denomenators are 5b and 7b^3c 5b=5 and b 7b^3c=7 times b times b times b times c LCM=7 times 5 times b times b times b times c=7b^3c=7cb^3
21. denomenator=5 and x+2 5=5 x+2=x+2 LCM=5 times (x+2)=5(x+2)=5x+10
22. denomenators are ab and b^2c ab=a time b b^2c=b times b times c LCM=a times b times b times c=ab^2c=acb^2
