初二年级数学一次函数的性质(第一课时）主讲人张娜北京市顺义区第十三中学1.一次函数的图象是一条直线.根据两点确定一条直线，只要确定两点坐标，就能画出一次函数的图象．复习2.一次函数的图象y=kx+b（k0)是经过点（0，b）和点（，0）的一条直线．当b=0时，是正比例函数y=kx，图象是经过原点（0，0）和点（1，k）的一条直线．复习bk复习3.画出一次函数y=x+2的图象（1）列表x-20y02（2）描点A（-2，0)，B（0，2）（3）连线oyx12345–1–2–3–4–512345–1–2–3–4–5y=x+2ABoyx12345–1–2–3–4–512345–1–2–3–4–5ABoyx12345–1–2–3–4–512345–1–2–3–4–5ABoyx12345–1–2–3–4–512345–1–2–3–4–5复习4.待定系数法先把所求的系数设为未知数，再根据所给的条件确定这些系数的方法，叫做待定系数法，它是确定函数表达式的一种常用方法．设列解代oyxy=12x+2y=x+2y=4x+212345–1–2–3–4–512345–1–2–3–4–5（1）（2）（3）oyxy=12x+2y=x+2y=4x+212345–1–2–3–4–512345–1–2–3–4–5yxoy=12x2y=12xy=12x+412345–1–2–3–4–512345–1–2–3–4–5三个一次函数所对应的图象是三条互相平行的直线.k相同b不同（1）yxoy=12x2y=12xy=12x+412345–1–2–3–4–512345–1–2–3–4–5k相同b不同（1）yxoy=12x2y=12xy=12x+412345–1–2–3–4–512345–1–2–3–4–5是不是一次函数表达式，在k值相同b值不同时，所对应的图象都是互相平行的直线呢？结论：一次函数y=kx+b(k0)，如果k值相同，而对于b的不同值，对应的图象是一组互相平行的直线．b=3.34oyxy=kx+bk=–1.5212345–1–2–3–4–512345–1–2–3–4–5b=1.82b=3.34oyxy=kx+bk=–1.5212345–1–2–3–4–512345–1–2–3–4–5b=0.62b=1.82b=3.34oyxy=kx+bk=–1.5212345–1–2–3–4–512345–1–2–3–4–5b=–0.70b=0.62b=1.82b=3.34oyxy=kx+bk=–1.5212345–1–2–3–4–512345–1–2–3–4–5b=–0.70b=0.62b=1.82b=3.34oyxy=kx+bk=–1.52b=–1.5212345–1–2–3–4–512345–1–2–3–4–5三个一次函数所对应的图象交于y轴同一点（0，2）．b相同k不同oyxy=12x+2y=x+2y=4x+212345–1–2–3–4–512345–1–2–3–4–5（2）b相同k不同是不是一次函数表达式，在b值相同k值不同时，所对应的图象都交于y轴同一点呢？oyxy=12x+2y=x+2y=4x+212345–1–2–3–4–512345–1–2–3–4–5（2）结论：一次函数y=kx+b(k0)，如果b值相同，而对于k的不同值，对应的图象是...
