#3.
√18²-5.7² Second Choice
#4
l²=5²+4² = 25+16 = = 41
l=√41
l= 6.4
Second Choice
#5 Only A --- First choice
#7 6 ----- Third choice
#8 V=

942 units³ ---Second choice
At first, she had +2y in the upper and -5y in the lower.
She multiplied the upper by 5 . Then she had +10y in the upper.
She should multiply the lower by 2 . Then she'll have -10y
there. She'll be able to add the two equations, and the 'y's will
go away. She'll be left with a single equation with only 'x' in it,
and she can solve that one for the value of 'x'.
Answer:

Step-by-step explanation:
Since we know we only have 640 feet of fence available, we know that L + W + L = 640,
2L + W = 640. This allows us to represent the width, W, in terms of L: W = 640 – 2L
Remember, the area of a rectangle is equal to the product of its width and length, therefore,
Notice that, quadratic has been vertically reflected, since the coefficient on the squared term is negative, so the graph will open downwards, and the vertex will be a maximum value for the area.
recall,
Since our function is A(L)=640L-2L², we get
plug in the value of a and b into the first formula:


hence,the dimensions of the pen that will maximize the area are<u> </u><u>L=</u><u>1</u><u>6</u><u>0</u><u>m</u><u> </u>and<u> </u><u>W=</u><u>7</u><u>6</u><u>8</u><u>0</u><u>0</u><u>/</u><u>1</u><u>6</u><u>0</u><u>=</u><u>4</u><u>8</u><u>0</u><u>m</u>
and we're done!