如圖,直線一次函數(shù)y=kx+b的圖象,填空:
(1)b=______,k=______;
(2)當(dāng)x=30時(shí),y=______;
(3)當(dāng)y=30時(shí),x=______.
(1)根據(jù)圖形可得函數(shù)過點(diǎn)(2,0)和(0,2),
將這兩點(diǎn)代入得:
,
解得:k=-1,b=2.
(2)由(1)得函數(shù)解析式為:y=-x+2,
∴當(dāng)x=30時(shí),y=-28;
(3)當(dāng)y=30時(shí),x=-28.
故答案為:2,-1;-28;-28.