If f(x)=x(x+1), find the value of:
(a) 2f(-4) (b) f(2)+[f(-3)]^2

(a)我識計到2f(-4)=12, 但答案係24 @@" 個個2除左又唔答bor..應該點計..? With explain thx
(b)直頭唔識計

thx a lot
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另問:
(I)A bag contains $2 coins and $5 coins, and there are altogether 6 coins in the bag. Let n be the number of $2 coins and $A be the total amount of coins in the bag. A is a function of n.
(II)A piece of wire 20 cm long is bent into a rectangle. Let x cam and A cm^2 be the length and the areas of the rectangle respectively. A is a function of x.
Consider the function in each of the above cases. Find:
(a) its algebraic representation, (b) its domain

我想問點解(a) Case (I) 個答案會係A=30-3n, 而case (II)就係A=(10x)-(x^2)??
個答案堆數字係點黎??

tridentenviro :If f(x)=x(x+1), find the value of:
(a) 2f(-4) (b) f(2)+[f(-3)]^2

(a)我識計到2f(-4)=12, 但答案係24 @@" 個個2除左又唔答bor..應該點計..? With explain thx
(b)直頭唔識計

thx a lot

f(x)=x(x+1)
所以f(-4)=(-4)(-4+1)
(即係x變-4)

(a) 2f(-4)
=2(-4)(-4+1)
=(-8)(-3)
=24

(b)一樣照代