1X3X5+2X6X10+4X12X20+7X21X35 /1X5X7+2X10X14+4X20X28+7X35X49

=3+6+12+21 /7+14+28+49

=42 /98=3/7

Bài này chỉ có thể tính bình thường đc thôi ak, nếu muốn lời giải chuẩn thì tham khảo nhé!

\(\frac{1x3x5+2x6x10+4x12x20+7x21x35}{1x5x7+2x10x14+4x20x28+7x35x49}\)

Nhận xét:

a)Phần tử số:

2x6x10= (1 x 2) x (3x2) x (5x2) = (2x2x2) x (1x3x5)

4x12x20= (1x4) x (3x4) x (5x4) = (4x4x4) x (1x3x5)

7x21x35= (1x7) x (3x7) x (5x7) = (7x7x7) x (1x3x5)

b)Phần mẫu số:

2x10x14= (1x2) x (5x2) x (7x2) = (2x2x2) x (1x5x7)

4x20x28= (1x4) x (5x4) x (7x4) = (4x4x4) x (1x5x7)

7x35x49= (1x7) x (5x7) x (7x7) = (7x7x7) x (1x5x7)

Vậy:

        \(\frac{1x3x5+2x6x10+4x12x20+7x21x35}{1x5x7+2x10x14+4x20x28+7x35x49}\)

\(=\frac{\left(1x3x5\right)+\left(2x2x2\right)x\left(1x3x5\right)+\left(4x4x4\right)x\left(1x3x5\right)+\left(7x7x7\right)x\left(1x3x5\right)}{\left(1x5x7\right)+\left(2x2x2\right)x\left(1x5x7\right)+\left(4x4x4\right)x\left(1x5x7\right)+\left(7x7x7\right)x\left(1x5x7\right)}\)

\(=\frac{\left(1x3x5\right)x\left(1+2x2x2+4x4x4+7x7x7\right)}{\left(1x5x7\right)x\left(1+2x2x2+4x4x4+7x7x7\right)}\)

\(=\frac{1x3x5}{1x5x7}\)\(=\frac{3}{7}\)

đề bài ghi gì vậy bạn

liên minh phân số @@@

A = \(\frac{1.3.5+2.6.10+4.12.20+7.21.35}{1.5.7+2.10.14+4.20.28+7.35.49}\)

A = \(\frac{1.3.5.\left(1+8+64+343\right)}{1.5.7.\left(1+8+64+343\right)}\)

A = \(\frac{1.3.5}{1.5.7}\)

A = \(\frac{3}{7}=\frac{231}{539}\)

B = \(\frac{308}{708}=\frac{77}{177}=\frac{231}{531}\)

Vì \(\frac{231}{539}

mấy bạn bị ngu à

Ta có:

1×3×5 + 2×6×10 + 4×12×20 + 7×21×35/1×5×7 + 2×10×14 + 4×20×28 + 7×35×49

= 1×3×5×(1x1x1 + 2×2×2 + 4×4×4 + 7×7×7)/1×5×7×(1×1×1 + 2×2×2 + 4×4×4 + 7×7×7)

= 3/7 = 300/700 = 1 - 400/700

308/708 = 1 - 400/708

Vì 400/700 > 400/708

=> 1 - 400/700 < 1 - 400/708

=> 3/7 < 308/708

So sánh vs 308/708 hợp lí hơn đó bn

\(\frac{1.3.5+2.6.10+4.12.20+7.21.35}{1.5.7+2.10.14+4.20.28+7.35.49}=\frac{3.5+\left(4.12.4\right)5+\left(2.6.2\right).5+\left(7.21.7\right).5}{5.7+\left(2.2.14\right).5+\left(4.4.28\right).5+\left(7.7.49\right).5}\)

mk gợi ý thôi bạn tự làm tiếp

308phan 708 lon hon vi ta tinh theo cach gach roi so sanh