23.已知有理數(shù)a,b,c在數(shù)軸上所對(duì)應(yīng)的點(diǎn)分別是A、B、C三點(diǎn),且a、b、c滿足:
①多項(xiàng)式x
|a|+(a-2)x+7是關(guān)于x的二次三項(xiàng)式;
②(b-1)
2+|c-4|=0.
(1)直接寫出a,b,c的值;
(2)點(diǎn)P為數(shù)軸上C點(diǎn)右側(cè)一點(diǎn),且點(diǎn)P對(duì)應(yīng)的數(shù)為y,化簡(jiǎn)|y+2|+|1-y|-|y-4|;
(3)點(diǎn)A在數(shù)軸上以每秒1個(gè)單位長(zhǎng)度的速度向左運(yùn)動(dòng),同時(shí)點(diǎn)B和點(diǎn)C在數(shù)軸上分別以每秒1個(gè)單位長(zhǎng)度和3個(gè)單位長(zhǎng)度的速度向右運(yùn)動(dòng),設(shè)運(yùn)動(dòng)時(shí)間為t秒,若在整個(gè)運(yùn)動(dòng)的過(guò)程中,BA-BC的值是否隨t的變化而變化?若不變,求出其值;若變化,說(shuō)明理由.