Toán Lớp 7: chứng tỏ rằng:2a+5b:3a–4b=2c+5d:3c–4d

Question

Toán Lớp 7:  chứng tỏ rằng:2a+5b:3a–4b=2c+5d:3c–4d

kimoanh34 · Answer

( dfrac{2a+5b}{3a-4b}= dfrac{2c+5d}{3c-4d} )    =>     ( dfrac{2a+5b}{3a-4b}- dfrac{2c+5d}{3c-4d} )    =>     ( dfrac{a+b}{a-b}- dfrac{c+d}{c-d} ) (1)   M&agrave;     ( dfrac{a}{b}= dfrac{c}{d} )    =>     ( dfrac{a}{c}= dfrac{b}{d} ) (2)   =>     ( dfrac{a-b}{c-d} )    v&agrave;     ( dfrac{a+b}{c+d} ) (3)   Từ (2) v&agrave; (3)   =>     ( dfrac{a-b}{c-d} )    =     ( dfrac{a+b}{c+d} )    =     ( dfrac{a}{b}= dfrac{c}{d} )    =>     ( dfrac{a-b}{c-d} )    =     ( dfrac{a+b}{c+d} ) = >     ( dfrac{a-b}{a+b} )    =     ( dfrac{c-d}{c+d} )    =>     ( dfrac{a+b}{a-b}= dfrac{c+d}{c-d} ) =     ( dfrac{a+b}{a-b}- dfrac{c+d}{c-d} ) (4)   Từ (1) v&agrave; (4)   =>     ( dfrac{2a+5b}{3a-4b}= dfrac{2c+5d}{3c-4d} ) ( đpcm)