dhhmsj
幼苗
共回答了18个问题采纳率:94.4% 举报
1.
按照三角型来算
AD^2+BD^2=AB^2
AB=15; AB^2 = 225
BD = 0.6AD 因为 AD/BD = 1/0.6
AD^2 + (.6AD)^2 = 225m
AD^2 + .36AD^2 = 225m
1.36AD^2 = 225m
AD = 12.86m
DE = BC = 2m
AE = AD + DE = 14.86m
因无图,只是臆测AB,BD,AD是直角三角形,然后DE为地面到D的距离,与BC平行相等.
2.
我猜根号包含(2/a)、(a/2)和(18a)
因为我不知道根号怎么打,将以^(1/2),意为的二分之一次方来表达平方根
a(2/a)^(1/2) = (2a)^(1/2)
2(a/2)^(1/2) = (2a)^(1/2)
(18a)^(1/2) = (9)^(1/2) * (2a))^(1/2) = 3(2a)^(1/2)
和则为:5(2a)^(1/2) = 10
(2a)^(1/2) = 2 平方等号左右边,得
2a = 4, a = 2
3.
晕,请你下次必定加入括号
猜为 1/6 * x * (18x)^(1/2) - x^2 * (1/2x)^(1/2)
1/6 * x * (18x)^(1/2) = (18/36 * x^3))^(1/2) = (1/2 * x^3)^(1/2), x 进根号时变为x^2
x^2 * (1/2x)^(1/2) = (1/2 * x^4/x)^(1/2) = (1/2 * x^3)^(1/2)
两式相等,所以左减右为零.
4.
(b/2)^(1/2) - (8b)^(1/2)
(8b)^(1/2) = (16 * b/2)^(1/2) = 4(b/2)^(1/2)
(b/2)^(1/2) - 4(b/2)^(1/2) = -3(b/2)^(1/2)
5.
同3.
ab 进根号变为 (ab)^2 = a^2 * b^2
1/(ab) * (9ab^3)^(1/2) = 3(b/a)^(1/2)
3(b/a)^(1/2) - 2(b/a)^(1/2) = (b/a)^(1/2)
6.
最后这题有点变态
计算机给的答是12
可以用已知方程式(a+b)(a-b) = a^2-b^2来求答
例1/(1+√3) = (1-√3)/(1-3) = (1-√3)/(-2)
同样,后面的步骤变为
(√(2x-1) - √(2x+1))/(-2)
相加所有数,则为
(1-√625)/(-2)中间的全部都自动消掉
√625 = 25
1-25 = -24
-24/-2 = 12
1年前
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