solve each of the following equations using any method.
(leave the answer in surd form if necessary)
1.(x+4)^2=15 (answer: -4+開方１５, -4-開方15)
我想知點解要抽個數出黎,(好似化到最簡)
即(x+4)^2=15
x^2+8x+16=15
.......................
點解一d數又唔洗既??
e.g. 4x^2-0.6x-0.5=0 (呢個又唔洗)
quadratic equations
2008-10-20 6:53 pm
回答 (3)
2008-10-20 7:32 pm
✔ 最佳答案
(x+4)^2=15 (x+4)=root15
x=-4+root15 or-4-root15
我唔知你講gei抽個數出黎係咪尼個..↓
(x+4)^2=15化解成x^2+8x+16=15..
如果係你會將條數複雜化..
因為root15係無理數..
點解(4x^2-0.6x-0.5=0)尼個又唔洗呢...
係因為4x^2-0.6x-0.5可以分解成解(2x-5)(2x+1)..
希望幫到你!!=)
2008-10-21 4:28 am
因為公式是:
(-b±√(b^2-4ac))/2a=0
所以要抽個數出黎
(-b±√(b^2-4ac))/2a=0
所以要抽個數出黎
2008-10-20 7:40 pm
Because you should at first re-write the equation to its standard form : ax^2 + bx + c = 0.
For (x + 4)^2 = 15. There are 2 methods:
(1) Re-write to standard form x^2 + 8x + 16 = 15
That is x^2 + 8x + 1 = 0, so x = [-8+/-sqrt(64 - 4)]/2 = - 4 +/- sqrt 15.
(2) Using identity.
(x+4)^2 - 15 = 0
(x +4)^2 - (sqrt15)^2 = 0
[(x + 4) + sqrt15][(x + 4) - sqrt 15] = 0
So x = -4 +/- sqrt 15.
For (x + 4)^2 = 15. There are 2 methods:
(1) Re-write to standard form x^2 + 8x + 16 = 15
That is x^2 + 8x + 1 = 0, so x = [-8+/-sqrt(64 - 4)]/2 = - 4 +/- sqrt 15.
(2) Using identity.
(x+4)^2 - 15 = 0
(x +4)^2 - (sqrt15)^2 = 0
[(x + 4) + sqrt15][(x + 4) - sqrt 15] = 0
So x = -4 +/- sqrt 15.
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