# How do I multiply two elements?

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Beenish Shabir on 16 Oct 2020
Commented: Rik on 19 Oct 2020
This question was flagged by Image Analyst

#### 1 Comment

Rik on 19 Oct 2020
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.
alpha = (1:90)
b = a * cosd(alpha(1:90));
area = 0.5*a*sind(1:90)
triangle= area*b

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:
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 on 17 Oct 2020
Thank you so much!! You are such a life saver :)
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.

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 Comment

Beenish Shabir on 17 Oct 2020
omg thank u it works now!