A few days ago

Tofuie

quadratic equation (?) problem?

wanda determines that the expression A= -2w^2 + 36w models the area of a rectangular puppy run, where w is the width in metres, and A is the area in square metres. what dimensions produce an area of 112m^2?

My work: A= -2w^2 +36w -112

then i plugged it into the quadratic formula and got roots of 14 and 4. but 14^2 and 4^2 don’t equal 112….

can anyone plz explain what im doing wrong? thanks!

Top 3 Answers

A few days ago

Stasia Everila

Favorite Answer

A = -2w^2 + 36w

112 = -2(14)^2 + 36(14)

112 = -2(196) + 36(14)

112 = -392 + 504

112 = 112

You got the right answer, you just did your check wrong.

A few days ago

mara_malaluan

I factored the equation 0= -2w^2+36w-112 into 0= -(2w-28)(w-4) which has roots of 4 and 14…then I also tried the quadratic formula and I got the same results..maybe your checking is wrong..

Here’s my checking:

for the root of 14..

0= -2(14)^2+36(14)-112

0 = -392+504 – 112

0=504-504

0=0 =>then 14 is correct..

for 4:

0= -2(4)^2+36(4)-112

0= -32+144-112

0=144-144

0=0 =>then 4 is also correct..

Hope this helps..

A few days ago

lord_ssa

A = -2w2 + 36w

112 = -2w2 + 36w

-2w2 + 36w -112 = 0 (/-2)

w2 – 18w + 56 = 0

delta = 324 – 224 = 100

w’ = (18 – 10)/2 = 4

if you plugged the roots should be A = 0 not 112, because w’ and w” are roots.

vlw.

w” = (18 + 10)2 = 14

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