Toán Lớp 8: 1.(x+y)² 6.(5x-y)² 2.(x-2y)²

Question

Toán Lớp 8:  1.(x+y)²                                                                                            6.(5x-y)² 2.(x-2y)²                                                                                           7.(x+1/4)² 3.(xy²+1) (xy²-1)                                                                              8.(1/3 x - 1/2 y )² 4.(x+y)² (x-y)                                                                                    9.(3x+1) (3x-1) 5.(2x+3y)²                                                                                        10.(x²+2/5 y) (x² - 2/5 y)

dinhcongson · Answer

Giải đáp:      1) $(x + y)^{2}$     $= x^{2} + 2xy + y^{2}$     2) $(x - 2y)^{2}$     $= x^{2} - 2.x.2y + 4y^{2}$     3) $(xy^{2} + 1)(xy^{2} - 1)$     $= (xy^{2})^{2} - 1$     $= x^{2}y^{4} - 1$     4) $(x + y)&sup2;.(x - y)$     $= (x + y)(x + y)(x - y)$     $= (x + y)(x^{2} - y^{2})$     $= x^{3} - xy^{2} + xy^{2} - y^{3}$     $= x^{3} - y^{3}$     5) $(2x + 3y)^{2}$     $= 4x^{2} + 12xy + 9y^{2}$     6) $(5x - y)^{2}$     $= 25x^{2} - 10xy + y^{2}$     7) $(x +  dfrac{1}{4})^{2}$     $= x^{2} +  dfrac{1}{2}x +  dfrac{1}{16}$     8) $( dfrac{1}{3}x -  dfrac{1}{2}y)^{2}$     $=  dfrac{1}{9}x^{2} -  dfrac{1}{3}xy +  dfrac{1}{4}$     9) $(3x + 1)(3x - 1)$       $= 9x^{2} - 1$     10) $(x^{2} +  dfrac{2}{5}y)(x^{2} -  dfrac{2}{5}y)$     $= (x^{2})^{2} - ( dfrac{2}{5}y)^{2}$     $= x^{4} -  dfrac{4}{25}y^{2}$

ngoclandiep · Answer

Đáp án:       Giải thích các bước giải: