the size of a TV screen is given as the length of the screen' s diagonal. If the sceens were flat, then the area of a square 21-inch sceen would be how many inches greater than the area of a squre 19-inch sceen?
a. 2 b. 4 c. 16 d. 38 e.40
此题的意思是不是说:21 村的面积比19 村大多少?21,19 分别是对角线。怎么得出E?
设21寸的边长为A,设19寸的边长为B
因为题目已经说明了电视为正方形,现在要求的是两个正方形的面积差
由正方形的定义可知:(A的平方)+(A的平方)=21的平方;(B的平方)+(B的平方)=19的平方
S21寸的面积=A 的平方 S19寸的面积=B的平方
可得:S21-S19=21的平方/2-19的平方/2=40
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