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Which ordered pair in the form (a, b) is a solution of this equation?

7a – 5b = 28


A.
(4, 0)

B.
(0, 4)

C.
(–2, –3)

D.
(–3, –2)


Sagot :

[tex]A. \\ (4,0) \\ a=4 \\ b=0 \\ \Downarrow \\ 7 \times 4-5 \times 0 \stackrel{?}{=} 28 \\ 28-0 \stackrel{?}{=} 28 \\ 28\stackrel{?}{=} 28 \\ 28=28 \\ true[/tex]

[tex]B. \\ (0,4) \\ a=0 \\ b=4 \\ \Downarrow \\ 7 \times 0 - 5 \times 4 \stackrel{?}{=} 28 \\ 0-20 \stackrel{?}{=} 28 \\ -20 \stackrel{?}{=} 28 \\ -20 \not= 28 \\ not \ true[/tex]

[tex]C. \\ (-2,-3) \\ a=-2 \\ b=-3 \\ \Downarrow \\ 7 \times (-2) - 5 \times (-3) \stackrel{?}{=} 28 \\ -14+15 \stackrel{?}{=} 28 \\ 1 \stackrel{?}{=} 28 \\ 1 \not= 28 \\ not \ true[/tex]

[tex]D. \\ (-3,-2) \\ a=-3 \\ b=-2 \\ \Downarrow \\ 7 \times (-3) -5 \times (-2) \stackrel{?}{=} 28 \\ -21 +10 \stackrel{?}{=} 28 \\ -11 \stackrel{?}{=} 28 \\ -11 \not= 28 \\ not \ true[/tex]

The answer is A.