If 2x + 3y = 4 and 5x + 6y = 7, what is the value of 8x + 9y ?
A.) -10 B.) -1 C.) 2 D.) 7 E.) 10
Find the values of x and y from the given system of equations, then substitute those values into 8x + 9y.
Solve the system. 2x + 3y = 4 5x + 6y = 7 -4x - 6y = -8 {multiplied first equation by -2} 5x + 6y = 7 {second equation stays the same} ---------------- x = -1 {added the two equations} Substitute the value of x into one of the two equations to solve for y. 2x + 3y = 4 {first equation} 2(-1) + 3y = 4 {substituted -1, in for x, into first equation} -2 + 3y = 4 {multiplied 2 by -1} 3y = 6 {added 2 to each side} y = 2 {divided each side by 3} Substitute -1 for x and 2 for y, into the expression 8x + 9y. 8x + 9y = 8(-1) + 9(2) {substituted -1 for x and 2 for y} = -8 + 18 {multiplied} = 10 {added} E.) 10 Ask Algebra House Comments are closed.
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