Question 344324
By definition,
{{{A+C=90}}}
{{{A+S=180}}}
Subtracting,
{{{A+S-A-C=180-90}}}
{{{S-C=90}}}
.
.
.
{{{S=3C}}}
Substituting,
{{{3C-C=90}}}
{{{2C=90}}}
{{{C=45}}}
Then,
{{{A+45=90}}}
{{{highlight(A=45)}}}degrees