F4 math problems HELP~!!!

用戶3618

2007-06-03 8:41 pm

1.If the three sides of a triangle is in the ratio 5 : 6 : 7and the area of the triangle is 150√6 cm^2, then the perimeter of the triangle is
A.72cm B. 90cm C.108cm D.198cm

2.If log(p - q) = logp - logq, then
A. p - q =1 B. p = q/1 - q C.p = q^2/ q -1 D. p = q/1+q

3. Let f(x) = x^2 such that x is real. If f(k) = f (k +1), k =
A. -1/2 B.0 C.1 D.1/2

更新1:

4.In the figure, EFGH is the top face of a cube on which M is the mid-point of diagonal EG.Find the angle between the lines BH and BM. A.24° B.30° C.45° D. 60° Figure http://server6.pictiger.com/img/221734/picture-hosting/--.jpg

回答 (1)

So Much

2007-06-03 9:57 pm

✔ 最佳答案

set one of the side =x cm,

so,due to the ratio,they are 5x,6x,and 7x

s=a+b+c/2=(5x+6x+7x)/2=9x

the area=√s(s-a)(s-b)(s-c)
150√6=√[9x(9x-5x)(9x-6x)(9x-7)]
135000=9x 4x 3x 2x
135000=216x^4
x=+/-4

so,the side =20,24,28//

perimeter of the triangle is 72 (A)
---------------------------------------
If log(p - q) = logp - logq
i.e.logp - logq=log(q/p)
so
p-q=p/q
pq-q^2=p
pq-p=q^2
p(p-1)=q^2
p=q^2/(p-1)//(c)

-----------------------------------------
f(k)=k^2
f (k +1)=(k+1)^2=k^2+2k+1

f(k) = f (k +1),
k^2=k^2+2k+1
k=-1/2//(A)
------------------------------------------

參考: ME,,,,,,i will ans q4 later

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