Toán Lớp 6: a) (x +1)(y+2)=10 b)(x-1)(x+y)=15 c)(x²+14)(y-5)=-4 d)x+y+xy=21
Mọi người giúp em với????????????????????????
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 6: a) (x +1)(y+2)=10 b)(x-1)(x+y)=15 c)(x²+14)(y-5)=-4 d)x+y+xy=21
Mọi người giúp em với????????????????????????
Comments ( 2 )
a) (x + 1) (y + 2) = 10
⇒x (y + 2) + y = 8
⇒(x + 1) y = 8 – 2 x
⇒x y + 2 x + y + 2 = 10
⇒x y + 2 x + y – 8 = 0
⇒x + 1!=0, y = -(2 (x – 4))/(x + 1)
⇒x = -11, y = -3
⇒x = -6, y = -4
⇒x = -3, y = -7
⇒x = -2, y = -12
⇒x = 0, y = 8
_____________________________________
b) (x – 1) (x + y) = 15
⇒(x – 1) y = -x^2 + x + 15
⇒x^2 + x y – x – y – 15 = 0
⇒x^2 + x y – x – y = 15
⇒x – 1!=0, y = (-x^2 + x + 15)/(x – 1)
⇒x = ± 4, y = 1
⇒x = -14, y = 13
⇒x = -2, y = -3
⇒x = 0, y = -15
⇒x = 2, y = 13
_____________________________________
c) $\left(x²+14\right)\left(y-5\right)=-4$
$⇒x^2\:+14=-4\:$ hoặc $y-5=-4$
TH1: $x^2+14=-4$
$⇒x^2+14-14=-4-14$
$⇒x^2=-18$
$⇒x=\sqrt{-18},\:x=-\sqrt{-18}$
TH2: $y-5=-4$
$⇒y-5+5=-4+5$
$⇒y=1$
Vậy $x=±\sqrt{18}, y = 1$
_____________________________________
d) x + y + x y = 21
⇒x y + x + y – 21 = 0
⇒(x + 1) y = 21 – x
⇒x + 1!=0, y = (21 – x)/(x + 1)
⇒x = -23, y = -2
⇒x = -12, y = -3
⇒x = -3, y = -12
⇒x = -2, y = -23
⇒x = 0, y = 21
Ta có: 2x+12x+1 và y−5y−5 là ước của 12;12=1.12=2.6=3.4.12;12=1.12=2.6=3.4.
Vì 2x+12x+1 lẻ ⇒2x+1=1⇒2x+1=1hoặc 2x+1=32x+1=3.
+) 2x+1=1⇒x=0;y−5=12⇒x=0;y=17.2x+1=1⇒x=0;y−5=12⇒x=0;y=17.
+) 2x+1=3⇒x=1;y−5=4⇒x=1;y=9.2x+1=3⇒x=1;y−5=4⇒x=1;y=9.
Vậy (x;y)(x;y) là: 0,17; 1,9.