alleryStart learning →Solve for x: 2.8x + 12 = -1.4x - 9.
Ax = 15
Bx = -1.5
Cx = -5
Dx = 1.5
Answer & Solution
Correct answer: C. x = -5
1. Add 1.4x to both sides to collect the variable terms on the left: 2.8x + 1.4x + 12 = -9.
2. Combine like terms: 4.2x + 12 = -9.
3. Subtract 12 from both sides: 4.2x = -21.
4. Divide both sides by 4.2: x = -21 / 4.2.
5. Compute: x = -5.
6. Check: 2.8(-5) + 12 = -14 + 12 = -2 and -1.4(-5) - 9 = 7 - 9 = -2, so both sides agree.
7. x = -1.5 comes from subtracting the decimals as 1.4 instead of adding them, and x = 1.5 also drops the sign; x = 15 misplaces the decimal point in the final division.
_Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 2 "Solving Linear Equations and Inequalities", section 2.3 Solve Equations with Variables and Constants on Both Sides_
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