if 2 sides av triangel the same, its isosales triangel
sound like bas=2.5 & 2 equal side=15...tall point, like speer hed
Yu draw vertikal line from mid av base up tu point=rite triangel
1 side=2.5/2=1.25, other side=15=diagonal
get hite from 15^2 -1.25^2
15^2=225, 1.25^2=1.5625; differ=223.4375
Hite=14.9478
Yu kan get base angel=invers tangent 14.9478/1.25 (=11.9583)
85.22 deg
Both bas angels the same
So top angel=180-170.44=10deg