Y A =4× 10+5(x-4)？
=20+5x, where x> is four.
Y b =0.9(4× 10+5x)
=36+4.5x？ Among them, x> IV
(2) Draw an image according to the function formula.
The intersection of these two formulas is
(32, 180)? There is something wrong with the image coordinates in the topic.
According to the image, when 4
When x & gt=32 when? Cost-effective according to B.
That is to say, when the number of exercise books purchased is between 4 and 32, method A is more favorable;
When the number of exercise books purchased is 32 or more, the second method is more favorable.