D为斜边AB的中点,DE垂直于AB交BC于E,
△BDE≌△ADE,
∠DBE=∠DAE.
设∠EAC=2x,则∠DAE=5x,∠DBE=5x,
角C为90度,∠CAB+∠CBA=90度,
2x+5x+5x=90,
x=7.5,
∠BAC=7x=52.5°.