1 Tính nhanh
1) 1001 ² 2) 29,9.30,1 3) 201 ²
2) Tìm x
1) 25x ² – 9=0 2) (x-3) ² – 4=0 3) 2 ² 2x=24
1 Tính nhanh 1) 1001 ² 2) 29,9.30,1 3) 201 ² 2) Tìm x 1) 25x ² – 9=0 2) (x-3) ² – 4=0 3)
By Parker
1, Tính nhanh
1001 ²=(1000+1)²=1000²+2.1000.1+1²
= 1000000 + 2000+1
=1002001
29,9.30,1=(30-0,1) (30+0,1)=30²-(0,1)²=900-0,01=899,99
201 ²=(200+1)²=200²+2.200.1+1²=40000+400+1=40401
2, Tìm x
25x ² – 9=0
⇔25x² – 3²=0
⇔(25x+3) (25x-3)=0
$\left \{ {{25x+3=0} \atop {25x-3=0}} \right.$
$\left \{ {{25x=0-3} \atop {25x=0+3}} \right.$ \(\left[ \begin{array}{l}x= \frac{-3}{25} \\x= \frac{3}{25} \end{array} \right.\)
(x-3) ² – 4=0
⇔[(x-3)²-2²]=0
⇔[(x-3)-2] [(x-3)+2]=0
[$\left \{ {{(x-3)-2=0} \atop {(x-3)+2=0}} \right.$ ]=0
$\left \{ {{x-3=2} \atop {x-3=-2}} \right.$ \(\left[ \begin{array}{l}x=5\\x=1\end{array} \right.\)
2 ² -2x=24
⇔2²- 2x-24=0
⇔x²-6x+4x-24=0
⇔(x²-6x)+(4x-24)=0
⇔x(x-6)+4(x-6)
⇔(x-6) (x+4)=0
$\left \{ {{x-6=0} \atop {x+4=0}} \right.$ \(\left[ \begin{array}{l}x=6\\x=-4\end{array} \right.\)