7)
I = (PRT) / (100)
315 = [ (500)(3.5)(T) ] / (100)
315 = (1750 T) / (100)
31500 = 1750T
T = 31500 ÷ 1750
T = 18
8)
s = [ m ( p-q) ] / (r)
5 = [ 2 ( p - 3 ) ] / 4
5 = ( 2p -6 ) / 4
20 = 2p - 6
26 = 2p
p = 13
9) 答案要两位数
V = W √(a² - x²)
30 = 5√(12² - x²)
提醒:5√12 它们关系是乘,所以不要写成 ⁵√12
6 = √(12² - x²)
6 = √(144 - x²)
6² = 144 - x²
36 =144 - x²
36 - 144 = -x²
-108 = -x²
两边减,变加
108 = x²
x = √(108)
x = 10.39 (两位数)
10)
V = (1/3) π r²h
45 = (1/3)( 3.142 )( r² )( 8 )
45 = 8.38r²
计算机你会算到 (3142/375) 不用怕,直接换小数 (8.38)
45 ÷ 8.38 = r²
5.37 = r²
r = √(5.37)
r = 2.32 (两位数)