+ + =2 0 (*)X AX B+ + + + = ⇔ + + =2 2( )( ) 0X AX B X BX A 2X BX...
Câu 2 :
a)
P= cos2
α −2 1 sin−2
α + =1 cos2
α−2 cos2
α +1cos2
2cos 1P=α
−α
+(vì cosα > 0)
(cos 1)2
P=α
−1 cosP= −α (vì cosα < 1)
b) (
4+ 15)(
5− 3)
4− 15 =(
5− 3) (
4+ 15) (
2
4− 15) = (
5− 3)
4+ 15= (
5− 3) (
2
4+ 15