Question

Use the given area A of the rectangle to find the value of x . A rectangle with its length labeled left-parenthesis 4 x plus 3 right-parenthesis feet and width labeled left-parenthesis 4 x minus 5 right-parenthesis feet. The area of the rectangle is 209 square feet.

Answer 1

Answer:

x = 4

Step-by-step explanation:

Length = (4x + 3) feet

Width = (4x - 5 )feet  

Area = Length x Breadth

209 = (4x + 3)(4x - 5)

209 = 4x( 4x -5) + 3 (4x -5)

$209 = 16x^2 -20x +12x -15\\\\0 = 16x^2 -8x -15 -209\\\\16x^2 -8x -224 = 0$

$Quadratic \ Equation \ with a = 16, b = -8, c = -224 \\\\x = \frac{-b \pm \sqrt{b^2 -4ac}}{2a}\\\\Substitute \ a, b, c \ in \ the \ equation.\\\\x = \frac{-b + \sqrt{b^2 -4ac}}{2a}, x =\frac{-b \ - \sqrt{b^2 -4ac}}{2a}\\\\x = \frac{8+ \sqrt{64 +14336}}{32}, x = \frac{8- \sqrt{64 +14336}}{32}\\\\x = \frac{8+ \sqrt{14400}}{32}, x = \frac{8-\sqrt{14400}}{32}\\\\x = \frac{8+120 }{32}, x= \frac{8-120}{32}\\\\x = \frac{128}{32} , x = \frac{-112}{32}\\\\x = 4 , x = \frac{-7}{2}$

Since measure of length or width cannot be negative, we take x = 4