La proportionnalité

y proportionnel à x lorsque avec a = constante appelée coefficient de proportionnalité.

y	0	4	8	12	16	20	24
x	0	1	2	3	4	5	6

Ici, on a .

Le graphique :

base64_ivborw0kggoaaaansuheugaaawoaaadbcaiaaabpfm0taaammkleqvr4no3dow_btbzgccobt9omvzphwea2fwtsqgvnu2hrvdzadaoslcssrflg_osati6mhgo7fmaqwdipqli04hecczk7dti4du5sfz9kazc2v7j1k7otpnfiacjfmt0agkyipgcurhwakin4afas8qggjoidqeneb4csia8ajrefaeoipgcurhxujpq9j0ueg64dcm8pi75p0x9te4jnn7opefdkffuy96jou4nqeb8v2w0nyy2pqoy3u9s5vxxn3eav2mmg4sn_xedfsvghfrz6nieewpx4fij3rm2xdis2bkk_q61nkiv7imdlo67mez4jau1bra6vgsyvbknr599k6izsq65dp3vhuveowrstbyk5_dd3ybidii_kza9erlbmh9d3kl0hjupkqtunpotveyjqu7e_ywtceukohuh_wnaufvqei0t6e6o9sxsmtbtlzii4fxm9idnskhba9yxirshyhmw_ds_7owyio4wipiqsc_aid83q95jk0d7tvyy_ul_sdadvzarlgdcxb9o6znxfbhpkqq_ovnl2vjm8div569kvmbyfld6dtqfhavfrkbxzh8kkxs7b81yf2gnwnj6yxyje0f5w9hc9pqdwfzebcdqhg_ijxp_f4igxn7m8rxxfnwumlt3njeoqhxvze_zleby_okhpnsjihrutt_lyizj6ke1_segoxxyyipnovtpjegc_u7q_vze_svcij270cx_rez7rx7vf3vffwrkpszlxsfp9z_84of_sqn8jeycb_5sl87ihlsc_1lyf2smwgnaphjyoy3wjhj4zqw8c89i_hqaa6wcv2cppvprinwkxt8rlnijklxvou5xzh2rf33qsrb3apk9lfaadkhvqvc0o8iig_8ce_aa6j_zl_qp9_ztf6lzh8s0it6azil44jb0vu0np1npzy1fpbalpvrvs9flaa2yit7ypwfskhsfhhsa2c4bh8ml_lh5anim8exrux8odqdktr952bfcbkbrby6pco0vnaegste_ctlj379_dy0dodk2xyeehi8vl79_boh0ds_f_82eb9f5z3u7_9rmgza5erbycvubrefqimqhwbkij4aler8acij_abqeveboctia0bjxaeakogpacurhwbkij4aler8acij_abqeveboctia0bjruijkute7_wgpta1g8fgmbiynqika_er_l5rstlxga6rbzpgeoqsdmrhidyv4c1fia90dfgra9p7vihgtqjjdj3wna1gm36_72hotk5mt7qzcwcveccwxac64vn5_erqqtfrsfritfxuac573rifad0vhhd3d1euer_5eoiwsjnp55exl67ryucqnzw6onr79q3zwuojpodayedo9xrj8dj0lfuipoaazwazvgahrhwatxh6erq4uoj3_60mdon4acomg2mwgewme9oz1iv4acoznu47ehws8qfuydqdnp2dnz2ddsq4joid2iskjul0anqwqym_gjimk8np6wk3g0mipocdtsatwwbwcxhx_phoehatia9gbyo4np6etm9ihvebvmp4po71egshjvgatpdbcxl5oz_ptc9if_idybdfecgxmyn4skpoarudpaiouru7izi2mlixjnabpuqebijy48cpdvkfx9xv1fpzs8gpgsfm2xird9hdtvusfovb21ucyyfmzn1qvgjtboob3jb64cmhgmmn5uodqmsy8ubngz0_vvvp9mtnyzbgxe6tmgmlbx1xffm5qa5vapg8cqtuixtvbzh8fhxsemhmor4qffm5_phckghb_zefkd9vfpxadqiocpefkdn2t1ubbzxgxbqqloxccqh2qy7tcxger9oj_l0en5_tnacdpgbnlcfow8pd6zn6rdia8328pdq2azi44gpnjxsdtw_pyc4tce_0dwujlqc_ectudhqfeidzubvoiwid1gtiqlraerw2in4gkvub_bwocq47gqqpklfo_8dicvls_1dckebwlb8bl4qoyxjxec3qckexwjxc3pjui7b0qhg4ip0_sc3b5346cbhcwrw9hq9m5ubxwjheik8iph3efh9cpv2dxsddtnhjx_1ttevx76yngg7ohx8qpdpygk7jt46rfugytwh6xgwm2ppvhdw0mwzwlhkihukj25xuli30hvdvxdudv2zu6ec4gmhogphqf9qdeidtxt6eii4won4qi1ubydb0ureb2pb4wgxeb_omownjdi6gphazvthkpvfhuf8oaktyytg6cdia3trvyeerwcrhyijwleqh9jzedzu9_seb4gp7eavjs5mm9ozwdzia9tfuurtmdyrh9he9qyshfhnpc5i5ld9eb82oxauwxmijzam4zioa7geh8shkt9_lsxvw8gwyhnzb28eb82kyu9eueowygtzmrh6huoi4idtoncg8hasxndl95avjkb_aiedi7kx6qsdxr37l0mpo6ojkwphcyweoo0z_lbfbysxjhk2yhk4inbllk9gapw9pj42prqab7io1v0wlhvvayuq3x0xww2o3au1si_2k_2bvb7fyid1si_2ozcudsk_ggnckdxamrh21a4iomhptqdwlecgphrbhsowgjio9kohivbxedtyfovggmger_nq28glef8naa9gban8deaem8gwqf7eb9wwywwfi7cwibii_q9_j62oxau9jnrlrz4qrjhos_ootv8_znxtalr_knhm2mhbyevsfqq_c4jqr_ijjqcmaqklxnese7ts_ozjjto1_fju9fpaqzrpoc94hquzprdwfz4fdya_xcxyh_i80i5gm9exj7nrrs6fiq_ugjkajkiook0bj8mstaxrhqpqk67rmjglkid4ostz_utikdia_doteqlqp8vg76xrkckcvii8aqd5aggotrhzu4uhhgd5atb7xutfz_3v_fk5wopwij8rqg4iuit4qmb6p_0_wyguit72onodz7oz6vmaqym_yoiiimjrgpjydywjgej8vjzeoer9fxath68h679c1yu4aj2r_ah9z8mt_latpugnbdyw0xxqcz_iktqtdzrx_pnzp7r8_px8fx1ncaabgdp4yetjrnwa15cfpapw9pb2luaania_vhzhkcfxd3dhbycwlfn4mf6v_p3790xzsxrpbaabgo06xtt9evj40hsdarsfdtldj25ns1mmcpt4_phgtw60qbfjq_yg9vt9ckebfxqrpigcbsrulfh4fhwkoibqtt8_zoho6ekpwqfuq83xozqk6q0e6tdo_kcpgfgxcpvqick_o9nfwbf8h9laoj4f_n7aky7afh80fqpfqt9zrjaeql54aamzypha6jkrcpx21o2jd5qkge1c3_oe8dasppr3rpcxk_6stnbpq3ymx2oca3il1aij5_yrjbeq7qmplthkmebveoghe8il7xgsp1vzv_0lj5okgz2t4yh_jiis0ut5gptiy8oikajeceblkcfruh7bqgsoocrmbe9pvq4krq8k4rjqzuvd4ddggowqqnwh1sca3yyer_hfp1jzsnfzdslxel29pbgaoxkqco5zo8r_pz5s7ygks6vr68jdsbortrglq_extun4jgo740anix5_hh5etk5ocm8uuxtp0_3akz39_fg8bhhomxufqoy5pk3fv2lly6m2el7r7p5tliu8erb7yyp04tlyvu5g_yejapz_nssd3jmyipyu_fv698jgp18wdzczvhs3m22o7x7iqpp3_vd5hhwwez_bzyrvhs3m22o7x6pvn6smqadbbmt6kt4hyyfl3akvev18f7c8pbnya2ni2bcbkczkishlt6epztumsetz5behnm263_njwdiwn7jwr9iufjjnzuafzxrnggpjbcnpzuonwx7nggcapb16dm263_njwwjiblb8mrhkeujy_ous3ykjiw8yngpqecgzddmvx7nx0mj7q23stio_e_hlapshxot60zwogvudzvonuekuprrlp_bw_lffh4qiyh00_wkro78flhfsch4hqcoht23taealrnp0egbycvnh4_kqzxedand6q18xzq_s2od5eynkgxm22ojywzby4pz51v3v6qvxltp0cgej8acij_abqeveboctia0bjxaeakv4hmq3evx46_9caaaaasuvork5cyii

Si en traçant y en fonction de x, on trouve une droite qui passe par l'origine,

situé sur la droite