Bài 21:
a)=√(37-35)(37+35)=√(2.72)=√144=12
b)=√(221-220)(221+220)=√441=21
c)=√(65-63)(65+63)=√(2.128)=√256=16
d)=√(117-108)(117+108)=√(9.225)=√9.√225=3.15=45
Bài 22:
a)=√2(√3+√5)/√7(√3+√5)=√2/√7
b)=(9√5+9√3)/(3√5+√3√3)=3(3√5+3√3)/(3√5+3√3)=3
c)=[√2+√3+2-√3(√2+√3+2)]/√2+√3+2
=(√2+√3+2)(1-√3)/√2+√3+2
=1-√3
Bài 23:
a)=√0,49.√a²=0,7a
b)=5.(7-a)=35-5a
b)=a².(a-2)=a³-2a²