a) 7 + 43 x 2 = 7 + 86 = 93

b) 8 + 15 : 3 = 8 + 5=13

c) 312 x 2 – 5 = 624 - 5= 619

d) 900 : 3 – 20= 300 -20=280

a,=(2a + b - 3c).(2a + b - 3c)

=4a\(^2\)+2ab-6ac+2ab+b\(^2\)-3bc-6ac-3cb+9c\(^2\)

=4a\(^2\)+b\(^2\)+9c\(^2\)+4ab

=2\(^2\).a\(^2\)+4ab+b\(^2\)+9c\(^2\)

=(2a+b)\(^2\)+9c\(^2\)( đáng lẽ chỗ này nó phải là -9c\(^2\) nhưng t ko ra đc )

b,=(a + 2b + 3c - 4d)(a + 2b + 3c - 4d)

=a\(^2\)+2ab+3ac-4ad+2ab+4b\(^2\)+6bc-8bd+3ac+6bc+9c\(^2\)-12cd-4ad-8bd-12cd+16d\(^2\)

=a\(^2\)+4b\(^2\)+9c\(^2\)+16d\(^2\)+4ab+6ac-8ad+12bc-16bd-24cd

=(a\(^2\)+4ab+4b\(^2\))+(9c\(^2\)-24cd+16d\(^2\))+6ac-8ad+12bc-16bd

=(a+2b)\(^2\)+(3c-4d)\(^2\)+2(3ac-4ad+6bc-8bd)

=(a+2b)\(^2\)+(3c-4d)\(^2\)+2[a(3c-4d)+2b(3c-4d)]

=(a+2b)\(^2\)+(3c-4d)\(^2\)+2(a+2b)(3c-4d)

khiếp bài dài nghoằng ra ý :(

a: \(\left(2a+b-3c\right)^2\)

\(=4a^2+b^2+9c^2+4ab-12ac-6bc\)

Đặt \(\dfrac{a}{b}=\dfrac{c}{d}=k\)

=>\(a=bk;c=dk\)

1: \(\dfrac{2a+3c}{2b+3d}=\dfrac{2\cdot bk+3\cdot dk}{2b+3d}=\dfrac{k\left(2b+3d\right)}{2b+3d}=k\)

\(\dfrac{2a-3c}{2b-3d}=\dfrac{2bk-3dk}{2b-3d}=\dfrac{k\left(2b-3d\right)}{2b-3d}=k\)

Do đó: \(\dfrac{2a+3c}{2b+3d}=\dfrac{2a-3c}{2b-3d}\)

2: \(\dfrac{4a-3b}{4c-3d}=\dfrac{4\cdot bk-3b}{4\cdot dk-3d}=\dfrac{b\left(4k-3\right)}{d\left(4k-3\right)}=\dfrac{b}{d}\)

\(\dfrac{4a+3b}{4c+3d}=\dfrac{4bk+3b}{4dk+3d}=\dfrac{b\left(4k+3\right)}{d\left(4k+3\right)}=\dfrac{b}{d}\)

Do đó: \(\dfrac{4a-3b}{4c-3d}=\dfrac{4a+3b}{4c+3d}\)

3: \(\dfrac{3a+5b}{3a-5b}=\dfrac{3bk+5b}{3bk-5b}=\dfrac{b\left(3k+5\right)}{b\left(3k-5\right)}=\dfrac{3k+5}{3k-5}\)

\(\dfrac{3c+5d}{3c-5d}=\dfrac{3dk+5d}{3dk-5d}=\dfrac{d\left(3k+5\right)}{d\left(3k-5\right)}=\dfrac{3k+5}{3k-5}\)

Do đó: \(\dfrac{3a+5b}{3a-5b}=\dfrac{3c+5d}{3c-5d}\)

4: \(\dfrac{3a-7b}{b}=\dfrac{3bk-7b}{b}=\dfrac{b\left(3k-7\right)}{b}=3k-7\)

\(\dfrac{3c-7d}{d}=\dfrac{3dk-7d}{d}=\dfrac{d\left(3k-7\right)}{d}=3k-7\)

Do đó: \(\dfrac{3a-7b}{b}=\dfrac{3c-7d}{d}\)

ai trả lời nhanh nhất đc tick nha

Bài 2: 

c: \(y:312=345:5\)

\(\Leftrightarrow y:312=69\)

hay \(y=21528\)

d: \(918670-y=251\cdot142\)

\(\Leftrightarrow y=91867-35642=56225\)

a) 67,2 : 7 = 9.6

b) 3,44 : 4 = 0.86

c) 42,7 : 7 = 6.1

d) 46,827 : 9 = 5.203

a, 9.6

b, 0.86

c, 6.1

d, 5.203

a) 67,2 : 7 = 9,6

b) 3,44 : 4 = 0,86

c) 42,7 : 7 = 6,1

d) 46,827 : 9 = 5,203

Tách ra đi bn

tách ra ik

dài wa'