a,b x 6 - a,b = 1a,b

a,b x 6 - a,b x 1 = 10 + a,b

a,b x ( 6 - 1 )     = 10 + a,b x 1

a,b x     5          = 10 + a,b x 1

a,b x     4          = 10

        a,b            = 10 : 4

        a,b            = 2,5

k minh nhe minh tra loi nhanh nhat va day du nhat . nho ket ban do nha

Ko hiểu đề bài

Đề yêu cầu gì nhỉ?

a: ƯCLN(a,b)=45

=>\(\left\{{}\begin{matrix}a=45k\\b=45c\end{matrix}\right.\)

Ta có: a+b=270

=>45k+45c=270

=>45(k+c)=270

=>k+c=6

=>\(\left(k;c\right)\in\left\{\left(1;5\right);\left(2;4\right);\left(3;3\right);\left(4;2\right);\left(5;1\right)\right\}\)

=>\(\left(a,b\right)\in\left\{\left(45;225\right);\left(90;180\right);\left(135;135\right);\left(180;90\right);\left(225;45\right)\right\}\)

mà ƯCLN(a,b)=45

nên \(\left(a,b\right)\in\left\{\left(45;225\right);\left(225;45\right)\right\}\)

b: \(ƯCLN\left(a,b\right)=5\)

=>\(\left\{{}\begin{matrix}a=5k\\b=5c\end{matrix}\right.\)

\(5k\cdot5c=300\)

=>\(25\cdot k\cdot c=300\)

=>\(k\cdot c=\dfrac{300}{25}=12\)

=>\(\left(k;c\right)\in\left\{\left(1;12\right);\left(12;1\right);\left(2;6\right);\left(6;2\right);\left(3;4\right);\left(4;3\right)\right\}\)

=>\(\left(a,b\right)\in\left\{\left(5;60\right);\left(60;5\right);\left(10;30\right);\left(30;10\right);\left(15;20\right);\left(20;15\right)\right\}\)

mà ƯCLN(a,b)=5

nên \(\left(a,b\right)\in\left\{\left(5;60\right);\left(60;5\right);\left(15;20\right);\left(20;15\right)\right\}\)

a) Ta có: a-b=6 => a=b+6

=>a.b = (b+6).b = 16

<=>b²+6b=16

<=>b²+6b-16=0

<=>(b-2).(b+8)=0

<=>\(\left[\begin{array}{nghiempt}b=2\\b=-8\end{array}\right.\)

=>\(\left[\begin{array}{nghiempt}a=8\\a=-2\end{array}\right.\)

=>\(\left[\begin{array}{nghiempt}a+b=10\\a+b=-10\end{array}\right.\)

Bạn xem lại đề bài phần b nhé.           

a) Ta có :  \(\left(a-b\right)^2=a^2-2ab+b^2=36\Rightarrow a^2+b^2=36+2ab=36+2.16=68\)

Lại có : \(\left(a+b\right)^2=a^2+2ab+b^2=68+2.16=100\Rightarrow a+b=\pm10\)

b) tương tự

b. a-b=5 =))
 

a: \(AB=\left(-2x^2+3x+5\right)\cdot\left(x^2-x+3\right)\)

\(=-2x^4+2x^3-6x^2+3x^3-3x^2+9x+5x^2-5x+15\)

\(=-2x^4+5x^3-4x^2+4x+15\)

b: Khi x=2 thì \(AB=-2\cdot16+5\cdot8-4\cdot4+4\cdot2+15\)

=-32+40-16+8+15

=15

1) ( a - b )² = a² - 2ab + b² = a² + 2ab + b² - 4ab = ( a + b )² - 4ab

                  = 7² - 4.5 = 49 - 20 = 29

2) ( a + b )² = a² + 2ab + b² = a² - 2ab + b² + 4ab = ( a - b )² + 4ab

                    = 5² + 4.3 = 25 + 12 = 37