# 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

1 view (last 30 days)
Beenish Shabir on 16 Oct 2020
Commented: Rena Berman on 7 May 2021
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
##### 2 CommentsShowHide 1 older comment
Rena Berman on 7 May 2021
(Answers Dev) Restored edit

Sign in to comment.

### Accepted Answer

Image Analyst on 16 Oct 2020
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);
##### 2 CommentsShowHide 1 older comment
Image Analyst on 17 Oct 2020
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.

Sign in to comment.

### More Answers (1)

meghannmarie on 16 Oct 2020
Edited: meghannmarie on 16 Oct 2020
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
##### 1 CommentShowHide None
Beenish Shabir on 17 Oct 2020
omg thank u it works now!

Sign in to comment.

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by