Evaluating an expression in terms of x:

How do I evaluate these expressions in terms of x?

1.) tan(2x-45degrees) 2.) sin(30degrees-3x)

also, how do I put the symbol for degrees? sorry im just new in matlab, thank you very much.

Answer 1

[Paulo Silva]

%make them anonymous functions
f1=@(x)tand(2*x-45) %notice that's not tan but tand, it uses degrees
f2=@(x)sind(30-3*x) %instead of radians

%evaluate at specific x values
x=0;
f1(x)
f2(x)

%plot them easily
subplot(211)   %create one axes to show the first function
ezplot(f1)     %you can define the x range like this ezplot(f1,[0 100])
subplot(212)   %create another axes to show the second function
ezplot(f2)     %ezplot(f2,[0 100]) -> this makes x start at 0 and finish at 100

[Fangjun Jiang]

Great! I learned sind() today!

[Dwyane Wade]

yeah thank you for teaching me sind too! By the way, when I use sind and the expression is: sind(2*x-45), does 2 also become in degree form? will this make the expression 2degrees*x-45degrees? I'm confused...

[Paulo Silva]

using sind all you put inside those () is in degree units, the word degrees means nothing to MATLAB.

[Dwyane Wade]

oh, but the problem is: tan(2x-45degrees). only 45 is in degree mode 2x are as is. How do I solve that?

[Paulo Silva]

tand(180*2*x/pi-45) or use Fangjun code

[Paulo Silva]

Conversions

rad -> deg

180*x/pi

deg -> rad

pi*x/180

[Fangjun Jiang]

You can't do degree*degree! Why not run an example?

x=90;

sind(x)

sind(2*x)

Answer 2

[Fangjun Jiang]

x=pi;
y=tan(2*x-pi*45/180)
z=sin(pi*30/180-3*x)

All the functions tan(), sin(), cos() etc use radius, you need to convert degree to radius.