How do I multiply two elements?

[Rik]

Question originally posted by Beenish Shabir (retrieved from Google cache):

I have a task where I have to calculate the area of a triangle from degrees 1 to 90, that is bound within a semi circle. I keep getting an error with the last line for some reason

I have a task where I have to calculate the area of a triangle from degrees 1 to 90, that is bound within a semi circle. I keep getting an error with the last line for some reason.

radius = rand;
a = 2*radius;
alpha = (1:90)
b = a * cosd(alpha(1:90));

area = 0.5*a*sind(1:90)

triangle= area*b

Answer 1

[Image Analyst]

You need to be using .* instead of * to do an elemenet by element multiplication instead of a matrix multiplication. Try this:

radius = 2 * rand;
alpha = (1:90)
bases = radius * cosd(alpha) % A vector of 90 elements
heights = radius * sind(alpha) % A vector of 90 elements
triangle_areas = 0.5 * bases .* heights % A vector of 90 elements
% For optional fun, plot the area.
plot(alpha, triangle_areas, 'b.-', 'LineWidth', 2);
grid on;
xlabel('Angle', 'FontSize', 18);
ylabel('Area', 'FontSize', 18);
title('Triangle Area vs. Angle', 'FontSize', 18);

[Beenish Shabir]

Thank you so much!! You are such a life saver :)

[Image Analyst]

You can Accept only one answer, so accept the best one. However you can also vote for that and the other(s) to award those persons additional reputation points also.

Answer 2

[meghannmarie]

You need to use the dot operator if you are doing element wise multiplication (.*). You use just the asterick for matrix multiplication.

triangle= area.*b

[Beenish Shabir]

omg thank u it works now!