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$A=(-135)\cdot29-13\cdot135+42\cdot(-65)$
$=(-135)\cdot29+13\cdot(-135)+42\cdot(-65)$
$=(-135)\cdot(29+13)+42\cdot(-65)$
$=(-135)\cdot42+42\cdot(-65)$
$=42\cdot(-135-65)$
$=42\cdot(-200)$
$=-8400$
= ( - 29) . 135 + 13 . 135 +( - 2730)
= 135 . [ ( - 29) + 13] + ( - 2730) mik nghĩ là như này
= 135 . ( - 16) + ( - 2730)
= ( - 2160) + ( - 2730)
= - 4890
a) 135 + 360 + 65 + 40 = (135 + 65) + (360 + 40) = 200 + 400 = 600.
b) 463 + 318 + 137 + 22 = (463 + 137) + (318 + 22) = 600 + 340 =940.
c) Nhận thấy 20 + 30 = 50 = 21 + 29 = 22+ 28 = 23 + 27 = 24 + 26.
Do đó 20 + 21 + 22 + ...+ 29 + 30
= (20+ 30) + (21 + 29) + (22 + 28) + (23 + 27) + (24 + 26) + 25
= 5 . 50 + 25 = 275.
BÀI LÀM:
a, 135 + 360 + 65 + 40 = ( 135 + 65 ) + ( 360 + 40 ) = 200 + 400 = 600
b, 463 + 318 + 137 + 22 = ( 463 + 137 ) + ( 318 + 22 ) = 600 + 340 = 940
c, 20 + 21 + 22 + ... + 29 + 30
= ( 20 + 30 ) + ( 21 + 29 ) + ( 22 + 28 ) + ( 23 + 27 ) + ( 24 + 26 ) + 25
= 50 . 5 + 25 = 275
\(A=\frac{595959}{454545}-\frac{14141414}{15151515}\)
\(A=\frac{595959:10101}{454545:10101}-\frac{14141414:1010101}{15151515:1010101}\)
\(A=\frac{59}{45}-\frac{14}{15}\)
\(A=\frac{59}{45}-\frac{42}{45}=\frac{17}{45}\)
\(B=\frac{65+891+135+909}{731-47+69-253}\)
\(B=\frac{\left(65+135\right)+\left(891+909\right)}{\left(731+69\right)-\left(47+253\right)}\)
\(B=\frac{200+1800}{800-300}=\frac{2000}{500}=4\)
a) (27+65)+(346-27-65)
= 27+65+346-27-65
= (27-27)+(65-65)+346
= 0 + 0 + 346
= 346
b) (42-69+17)-(42+17)
= 42-69+17 – 42 – 17
= (42-42)+(17-17)-69
= 0 + 0 – 69
= -69
a)(27+65)+(346-27-65)
=27+65+345-27-65
=(27-27)+(65-65)+346
=0+0+346
=346
b) (42-69+17)-(42+17)
=42-69+17-42-17
=(42-42)-69+(17-17)
=0-69+0
=-69
a, (18+29) +(158-18-29)
= 18+29+158-18-29
= (18-18) +(29-29)+ 158
= 158
b, (13-135+49)- (13+49)
= 13-135+49-13-49
= (13-13) +(49-49) -135
= 135
a, \(\left(18+29\right)+\left(158-18-29\right)\)
\(=18+29+158-18-29\)
\(=\left(18-18\right)+\left(29-29\right)+158\)
\(=158\)
b,
\(\left(13-135+49\right)-\left(13+49\right)\)
\(=13-135+49-13-49\)
= \(\left(13-13\right)+\left(49-49\right)-135\)
= \(-135\)
Bài1
a) 25/42 - 20/63 =5/18
b) 9/50 - 13/75 - 1/6 = -4/25
c) 2/15 - 2/65 - 4/39 = 0
Bài2
a) x + 7/12 =17/18-1/9 b) 29/30 - (18/23 + x)=7/69
x + 7/12 = 5/6 18/23 + x =29/30 - 7/69
x =5/6 - 7/12 18/23 +x = 199/230
x = 1/4 x = 199/230 - 18/23
x= 19/230
\(a,\left(13+49\right)-\left(13-135\right)\)
= \(13+49-13+135\)
= \(13-13+49+135\)
= \(184\)
\(b,\left(18+29\right)+\left(158-18-29\right)\)
= \(18+29+158-18-29\)
= \(158\)
\(c,4.5^2-3.\left(24-9\right)\)
= \(4.25-\left(72-27\right)\)
= \(100.-45\)
= \(55\)
\(d,\left[93-\left(20-7\right)\right]:16\)
= \(\frac{93-20+7}{16}\)
= \(\frac{80}{16}\)
= \(5\)