# Math Help - limit & derivative

1. ## limit & derivative

hey guys having trouble with this question. any help?

Use f '(x) = lim h->0 f(x + h) - f(x)/h

to find dy/dx when y = 3x + 4.

much appreciated!

2. Originally Posted by jvignacio
hey guys having trouble with this question. any help?

Use f '(x) = lim h->0 f(x + h) - f(x)/h

to find dy/dx when y = 3x + 4.

much appreciated!
$f(x) = 3x + 4$.

$f(x + h) = 3(x + h) + 4$.

$f(x + h) - f(x) = 3h$.

$\frac{f(x+h)-f(x)}{h} = 3$.

$\lim_{h \rightarrow 0} \frac{f(x+h)-f(x)}{h} = \lim_{h \rightarrow 0} 3 = 3$.

3. Originally Posted by mr fantastic
$f(x) = 3x + 4$.

$f(x + h) = 3(x + h) + 4$.

$f(x + h) - f(x) = 3h$.

$\frac{f(x+h)-f(x)}{h} = 3$.

$\lim_{h \rightarrow 0} \frac{f(x+h)-f(x)}{h} = \lim_{h \rightarrow 0} 3 = 3$.
haha any way of explaining what u did ??? so i can do the others myself.

4. Originally Posted by jvignacio
haha any way of explaining what u did ??? so i can do the others myself.
That's about as plain as it will ever get! What don't you understand?

5. Originally Posted by mr fantastic
That's about as plain as it will ever get! What don't you understand?
actually its okay. i understand now. thank u