28.如圖1,在Rt△ABC中,∠ACB=90°,動(dòng)點(diǎn)M從點(diǎn)A出發(fā)沿A-C-B向點(diǎn)B勻速運(yùn)動(dòng),動(dòng)點(diǎn)N從點(diǎn)B出發(fā)沿B-C-A向點(diǎn)A運(yùn)動(dòng).設(shè)MC的長(zhǎng)為y
1(cm),NC的長(zhǎng)為y
2(cm),點(diǎn)M的運(yùn)動(dòng)時(shí)間為x(s),y
1、y
2與x的函數(shù)圖象如圖2所示.
(1)線段AC=
cm,點(diǎn)M運(yùn)動(dòng)
s后點(diǎn)N開(kāi)始運(yùn)動(dòng);
(2)求點(diǎn)P的坐標(biāo),并寫(xiě)出它的實(shí)際意義;
(3)當(dāng)∠CMN=45°時(shí),求x的值.